Appliance removal alarm system for motels

Abstract

A system for the prevention of the theft of televisions sets and other appliances from motels and the like requires the modification of the appliance by connecting a quartz crystal resonator across its terminals. A frequency-modulated oscillator connected to a transmission line linking all of the appliances is employed to stimulate the crystals in sequence. A transmit-receive switch operating at 100 herz frequency and phase detection between the oscillator and the echoes from the crystals improve selectivity, while a counter keeps track of the crystals heard from. An alarm and a visual display of a number indicate the time and place of a theft.

I claim: 
     
       1. A theft detection system for remote detection of the removal from a transmission line of any of a plurality of appliances, each of appliances having a pair of electrical terminals for connection to said transmission line, the combination of, a. a plurality of crystal resonators, each of said resonators being resonant at a frequency which is one of an ordered set of frequencies and different from the resonant frequency of the others of said plurality, each of said resonators being connected between a pair of said terminals to be set to ringing by application of a voltage at said one frequency to said pair, and   b. an alarm set remote from said appliances connected to said transmission line, said alarm comprising i. transmitter means including a variable voltage controlled oscillator for generating sequential electrical signals having substantial energy components at each of the resonant frequencies of said plurality of resonators,   ii. receiving means connected to said transmission line for detecting signals at each of said resonant frequencies,   iii. transmit-receive isolation means for connecting said transmitter means to said transmission line so that the energy components at said resonant frequencies generated by said transmitter means flow into said transmission line and are substantially prevented from flowing directly into said receiving means,   iv. multiplexing means for rendering said receiving means sensitive to said resonant frequencies according to a predetermined program of intervals and order,   v. alarm means connected to said receiver means responsive to a departure from said program, and   vi. counting means connected to said multiplexing means for counting signals corresponding to each detected resonant frequency.     
     
     
       2. A theft detection system for remote detection of the removal from a transmission line of any of a plurality of appliances, each of said appliances having a pair of electrical terminals for connection to said transmission line, the combination of, a. a plurality of resonators, each of said resonators being resonant at a frequency which is one of an ordered set of frequencies and different from the resonant frequency of the others of said plurality, each of said resonators being connected between a pair of said terminals to be set to ringing by application of a voltage at said one frequency to said pair, and   b. an alarm set remote from said appliances connected to said transmission line, said alarm comprising i. transmitter means for generating an electrical signal having substantial energy components at each of the resonant frequencies of said plurality of resonators,   ii. receiving means connected to said transmission line for detecting signals at each of said resonant frequencies,   iii. transmit-receive isolation means for connecting said transmitter means to said transmission line so that the energy components at said resonant frequencies generated by said transmitter means flow into said transmission line and are substantially prevented from flowing directly into said receiving means,   iv. multiplexing means for rendering said receiving means sensitive to said resonant frequencies according to a predetermined program of intervals and order, and   v. alarm means connected to said receiver means responsive to a departure from said program,     c. said transmitter means comprising an oscillator adapted for frequency modulation over a band of frequencies,   d. said receiving means comprising filter means selective of said band, a detector, and a low-pass circuit,   e. said resonant frequencies being uniformly spaced within said band,   f. said multiplexing means comprising a linear modulator for advancing the frequency of said oscillator regularly from one end of said band to the other slowly enough to excite in each of said resonators an unambiguous response,   g. said oscillator being a voltage-controlled oscillator having a center frequency of the order of 300 kiloherz,   h. said resonators being quartz crystals having resonant frequencies spaced by uniform intervals of substantially two kiloherz,   i. said filter having a pass band from 200 kiloherz to 400,   j. said detector being a phase detector responsive to changes in amplitude and phase as said oscillator is swept past one of said resonant frequencies, and a low pass circuit,   k. said transmit-receive isolations means comprising a switch and a multivibrator means for driving said switch alternately between a first state and a second state, said switch being arranged so that in its said first state, energy passes freely between said oscillator and said transmission line and transmission of signals through said filter is blocked, and in its said second state signals pass freely from said transmission line through said filter and flow of energy from said oscillator to said transmission line is blocked,   l. said modulator comprising a ramp generator to supply a modulating voltage to sweep said oscillator at a rate of the order of four kiloherz per second, and   m. said alarm means comprising i. a first trigger circuit for producing a counter-activating pulse at each time of crossing of said oscillator frequency and the resonant frequency of one of said resonators,   ii. a counter for accumulating the number of such crossings,   iii. a timer to mark the interval between said pulses, responsive to a delay significantly in excess of the programmed interval between said pulses to sound an alarm, stop the sweep of the ramp, and read out the accumulated number in said counter, and   iv. means for resetting said ramp generator upon said counter accumulating the cardinal number of resonators connected to said transmission said number being the sum of the number of said plurality and of control resonators part of said alarm set.     
     
     
       3. A theft detection system for remote detection of the removal from a transmission line of any of a plurality of appliances, each of said appliances having a pair of electrical terminals for connection to said transmission line, the combination of, a. a plurality of resonators, each of said resonators being resonant at a frequency which is one of an ordered set of frequencies and different from the resonant frequency of the others of said plurality, each of said resonators being connected between a pair of said terminals to be set to ringing by application of a voltage at said one frequency to said pair, and   b. an alarm set remote from said appliances connected to said transmission line, said alarm comprising i. transmitter means for generating an electrical signal having substantial energy components at each of the resonant frequencies of said plurality of resonators,   ii. receiving means connected to said transmission line for detecting signals at each of said resonant frequencies,   iii. transmit-receive isolation means for connecting said transmitter means to said transmission line so that the energy components at said resonant frequencies generated by said transmitter means flow into said transmission line and are substantially prevented from flowing directly into said receiving means.   iv. multiplexing means for rendering said receiving means sensitive to said resonant frequencies according to a predetermined program of intervals and order, and   v. alarm means connected to said receiver means responsive to a departure from said program,     c. said transmission means being a voltage controlled oscillator variable in frequency over a band about a center frequency of the order of 300 kiloherz,   d. said resonators being quartz crystals having resonant frequencies spaced by uniform intervals within said band,   e. said receiving means comprising an amplifier, a filter, for selectively passing said resonant frequencies and a phase detector responsive to changes in amplitude and phase as said oscillator is swept past one of said resonant frequencies, and a low pass circuit,   f. said transmit-receive isolation means comprising a switch and multivibrator means for driving said switch alternately between a first state and a second state, said switch being arranged so that in its said first state energy passes freely between said oscillator and said transmission line and transmission of signals through said filter is blocked, and in its said second state signals pass freely from said transmission line through said filter and flow of energy from said oscillator to said transmission line is blocked,   g. said multiplexing means comprising a ramp generator to supply a modulating voltage to sweep said oscillator at a rate of the order of four kiloherz per second, and   h. said alarm means comprising, i. a first trigger circuit for producing a counter activating pulse each time of crossing of said oscillator frequency and the resonant frequency of any of said resonators,   ii. a counter for accumulating the number of such crossings,   iii. a timer to mark the interval between said pulses, responsive to an interval significantly in excess of the programmed interval between said pulses to sound an alarm, stop the sweep of said ramp generator, and read out the accumulated number in said counter, and   iv. means for resetting said ramp generator upon said counter accumulating the cardinal number of resonators connected to said transmission line, said number being the sum of the number of said plurality and the number of control resonators part of said alarm set.     
     
     
       4. A theft detection system for remote detection of the removal from a transmission line of any of a plurality of appliances, each of said appliances having a pair of electrical terminals for connection to said transmission line, the combination of, a. a plurality of resonators, each of said resonators being resonant at a frequency which is one of an ordered set of frequencies and different from the resonant frequency of the others of said plurality, each of said resonators being connected between a pair of said terminals to be set to ringing by application of a voltage at said one frequency to said pair, and   b. an alarm set remote from said appliances connected to said transmission line, said alarm comprising i. transmitter means for generating an electrical signal having substantial energy components at each of the resonant frequencies of said plurality of resonators,   ii. receiving means connected to said transmission line for detecting signals at each of said resonant frequencies,   iii. transmit-receive isolation means for connecting said transmitter means to said transmission line so that the energy components at said resonant frequencies generated by said transmitter means flow into said transmission line and are substantially prevented from flowing directly into said receiving means,   iv. multiplexing means for rendering said receiving means sensitive to said resonant frequencies according to a predetermined program of intervals and order, and   v. alarm means connected to said receiver means responsive to a departure from said program,     c. said transmitted means being an oscillator variable in frequency over a band about a center frequency,   d. said resonators having resonant frequencies spaced by uniform intervals within said band,   e. said multiplexing means sweep the frequency of said oscillator at uniform rate across said band, and   f. said alarm means comprising, i. a first trigger circuit for producing a counter incrementing pulse each time of crossing of said oscillator frequency and the resonant frequency of any of said resonators,   ii. a counter for accumulating the number of such crossings, and   iii. a timer to mark the interval between said pulses, responsive to an interval significantly in excess of the programmed interval between said pulses to sound an alarm, stop the sweep, and read out the accumulated number.     
     
     
       5. A system as defined by claim 4 wherein c. said transmitter means comprises an oscillator adapted for frequency modulation over a band of frequencies,   d. said receiving means comprise filter means selective of said band, a detector, and a low-pass circuit,   e. said resonant frequencies are uniformly spaced within said band, and   f. said multiplexing means comprise a linear modulator for advancing the frequency of said oscillator regularly from one end of said band to the other slowly enough to excite in each of said resonators an unambiguous response.   
     
     
       6. A system as defined by claim 5, g. wherein said resonators are quartz crystals.   
     
     
       7. A system as defined by claim 5, g. wherein said transmit-receive isolation means comprise i. a switch having a first and a second state, connected to said transmitter means, said receiving means, and said transmission line, arranged so that in its first state energy passes freely between said transmitter means and said transmission line and is substantially barred from passing from said transmission line and from said transmitter means through said receiver means, and in its second state signals pass freely between said receiver means and said transmission line,   ii. together with driving means for periodically oscillating said switch between its said two states at intervals which are substantially briefer than the ringing time of said resonators, and substantially longer than the response time of said filter means.     
     
     
       8. A system as defined by claim 6, h. wherein said transmit-receive isolation means comprise, i. a switch having a first and a second state, connected to said transmitter means, said receiving means, and said transmission line, arranged so that in its first state energy passes freely between said transmitter means and said transmission line and is substantially barred from passing from said transmission line and from said transmitter means through said receiver means, and in its second state signals pass freely between said receiver means and said transmission line,   ii. together with driving means for periodically oscillating said switch between its said two states at intervals which are substantially briefer than the ringing time of said resonators, and substantially longer than the response time of said filter means.     
     
     
       9. A system as defined by claim 8 wherein, i. said ringing time is of the order of one-tenth second,   j. said response time is of the order of one-tenth of a millisecond,   k. said switching intervals are of the order of 10 milliseconds, and wherein   l. said oscillator frequency is advanced from one of said resonant frequencies to the next in the order of one second,   m. whereby a complete scanning cycle is completed in the order of one minute.   
     
     
       10. A system as defined by claim 8 wherein, i. said ringing time is more than 10 milliseconds,   j. said response time is less than one-tenth of a millisecond,   k. said switching intervals are between two and 50 milliseconds, and wherein   l. said oscillator frequency is advanced from one of said resonant frequencies to the next in less than one second.   
     
     
       11. A system as defined by claim 8 wherein said oscillator is a voltage-controlled oscillator. .Iadd.12. A detection system for remote detection of the presence in or absence from a transmission line of any of a plurality of resonators, each of said resonators being connectable with and disconnectable from said transmission line, the combination of, a. a plurality of crystal resonators, each of said resonators being resonant at a frequency which is one of an ordered set of frequencies and different from the resonant frequency of the others of said plurality, each of said resonators when connected with said transmission line being set to ringing by application of a voltage at said one frequency to said transmission line, and   b. an alarm set remote from said resonators connected to said transmission line, said alarm comprising, i. transmitter means including a variable voltage controlled oscillator for generating sequential electrical signals having substantial energy components at each of the resonant frequencies of said plurality of resonators,   ii. receiving means connected to said transmission line for detecting signals at each of said resonant frequencies,   iii. transmit-receive isolation means for connecting said transmitter means to said transmission line so that the energy components at said resonant frequencies generated by said transmitter means flow into said transmission line and are substantially prevented from flowing directly into said receiving means,   iv. multiplexing means for rendering said receiving means sensitive to said resonant frequencies according to a predetermined program of intervals and order,   v. alarm means connected to said receiver means responsive to a departure from said program, and   vi. counting means connected to said multiplexing means for counting signals corresponding to each detected resonant frequency. .Iaddend..Iadd.     
     
     
        3.  A detection system for remote detection of the presence in or absence from a transmission line of any of a plurality of resonators, each of said resonators being connectable with and disconnectable from said transmission line, the combination of, a. a plurality of crystal resonators, each of said resonators being resonant at a frequency which is one of an ordered set of frequencies and different from the resonant frequency of the others of said plurality, each of said resonators when connected with said transmission line being set to ringing by application of a voltage at said one frequency to said transmission line, and   b. an alarm set remote from said resonators connected to said transmission line, said alarm comprising, i. transmitter means for generating an electrical signal having substantial energy components at each of the resonant frequencies of said plurality of resonators,   ii. receiving means connected to said transmission line for detecting signals at each of said resonant frequencies,   iii. transmit-receive isolation means for connecting said transmitter means to said transmission line so that the energy components at said resonant frequencies generated by said transmitter means flow into said transmission line and are substantially prevented from flowing directly into said receiving means,   iv. multiplexing means for rendering said receiving means sensitive to said resonant frequencies according to a predetermined program of intervals and order, and   v. alarm means connected to said receiver means responsive to a departure from said program,     c. said transmitter means comprising an oscillator adapted for frequency modulation over a band of frequencies,   d. said receiving means comprising filter means selective of said band, a detector, and a low-pass circuit,   e. said resonant frequencies being uniformly spaced within said band,   f. said multiplexing means comprising a linear modulator for advancing the frequency of said oscillator regularly from one end of said band to the other slowly enough to excite in each of said resonators an unambiguous response,   g. said oscillator being a voltage-controlled oscillator having a center frequency of the order of 300 kiloherz,   h. said resonators being quartz crystals having resonant frequencies spaced by uniform intervals of substantially two kiloherz,   i. said filter having a pass band from 200 kiloherz to 400,   j. said detector being a phase detector responsive to changes in amplitude and phase as said oscillator is swept past one of said resonant frequencies, and a low pass circuit,   k. said transmit-receive isolations means comprising a switch and a multivibrator means for driving said switch alternately between a first state and a second state, said switch being arranged so that in its said first state, energy passes freely between said oscillator and said transmission line and transmission of signals through said filter is blocked, and in its said second state signals pass freely from said transmission line through said filter and flow of energy from said oscillator to said transmission line is blocked,   l. said modulator comprising a ramp generator to supply a modulating voltage to sweep said oscillator at a rate of the order of four kiloherz per second, and   m. said alarm means comprising, i. a first trigger circuit for producing a counteractivating pulse at each time of crossing of said oscillator frequency and the resonant frequency of one of said resonators,   ii. a counter for accumulating the number of such crossings,   iii. a timer to mark the interval between said pulses, responsive to a delay significantly in excess of the programmed interval between said pulses to sound an alarm, stop the sweep of the ramp, and read out the accumulated number in said counter, and     iv. means for resetting said ramp generator upon said counter accumulating the cardinal number of resonators connected to said transmission said number being the sum of the number of said plurality and of control   
     
     
        resonators part of said alarm set. .Iaddend..Iadd. 14.  A detection system for remote detection of the presence in or absence from a transmission line of any of a plurality of resonators, each of said resonators being connectable with and disconnectable from said transmission line, the combination of, a. a plurality of crystal resonators, each of said resonators being resonant at a frequency which is one of an ordered set of frequencies and different from the resonant frequency of the others of said plurality, each of said resonators when connected with said transmission line being set to ringing by application of a voltage at said one frequency to said transmission line, and   b. an alarm set remote from said resonators connected to said transmission line, said alarm comprising, i. transmitter means for generating an electrical signal having substantial energy components at each of the resonant frequencies of said plurality of resonators,   ii. receiving means connected to said transmission line for detecting signals at each of said resonant frequencies,   iii. transmit-receive isolation means for connecting said transmitter means to said transmission line so that the energy components at said resonant frequencies generated by said transmitter means flow into said transmission line and are substantially prevented from flowing directly into said receiving means,   iv. multiplexing means for rendering said receiving means sensitive to said resonant frequencies according to a predetermined program of intervals and order, and   v. alarm means connected to said receiver means responsive to a departure from said program,     c. said transmission means being a voltage controlled oscillator variable in frequency over a band about a center frequency of the order of 300 kiloherz,   d. said resonators being quartz crystals having resonant frequencies spaced by uniform intervals within said band,   e. said receiving means comprising an amplifier, a filter, for selectively passing said resonant frequencies and a phase detector responsive to changes in amplitude and phase as said oscillator is swept past one of said resonant frequencies, and a low pass circuit,   f. said transmit-receive isolation means comprising a switch and multivibrator means for driving said switch alternately between a first state and a second state, said switch being arranged so that in its said first state energy passes freely between said oscillator and said transmission line and transmission of signals through said filter is blocked, and in its said second state signals pass freely from said transmission line through said filter and flow of energy from said oscillator to said transmission line is blocked,   g. said multiplexing means comprising a ramp generator to supply a modulating voltage to sweep said oscillator at a rate of the order of four kiloherz per second, and   h. said alarm means comprising, i. a first trigger circuit for producing a counter activating pulse each time of crossing of said oscillator frequency and the resonant frequency of any of said resonators,   ii. a counter for accumulating the number of such crossings,   iii. a timer to mark the interval between said pulses, responsive to an interval significantly in excess of the programmed interval between said pulses to sound an alarm, stop the sweep of said ramp generator, and read out the accumulated number in said counter, and   iv. means for resetting said ramp generator upon said counter accumulating the cardinal number of resonators connected to said transmission line, said number being the sum of the number of said plurality and the number     
     
     
        of control resonators part of said alarm set. .Iaddend..Iadd. 15.  A detection system for remote detection of the presence in or absence from a transmission line of any of a plurality of resonators, each of said resonators being connectable with and disconnectable from said transmission line, the combination of, a. a plurality of crystal resonators, each of said resonators being resonant at a frequency which is one of an ordered set of frequencies and different from the resonant frequency of the others of said plurality, each of said resonators when connected with said transmission line being set to ringing by application of a voltage at said one frequency to said transmission line, and   b. an alarm set remote from said resonators connected to said transmission line, said alarm comprising, i. transmitter means for generating an electrical signal having substantial energy components at each of the resonant frequencies of said plurality of resonators,   ii. receiving means connected to said transmission line for detecting signals at each of said resonant frequencies,   iii. transmit-receive isolation means for connecting said transmitter means to said transmission line so that the energy components at said resonant frequencies generated by said transmitter means flow into said transmission line and are substantially prevented from flowing directly into said receiving means,   iv. multiplexing means for rendering said receiving means sensitive to said resonant frequencies according to a predetermined program of intervals and order, and   v. alarm means connected to said receiver means responsive to a departure from said program,     c. said transmitted means being an oscillator variable in frequency over a band about a center frequency,   d. said resonators having resonant frequencies spaced by uniform intervals within said band,   e. said multiplexing means sweep the frequency of said oscillator at uniform rate across said band, and   f. said alarm means comprising, i. a first trigger circuit for producing a counter incrementing pulse each time of crossing of said oscillator frequency and the resonant frequency of any of said resonators,   ii. a counter for accumulating the number of such crossings, and   iii. a timer to mark the interval between said pulses, responsive to an interval significantly in excess of the programmed interval between said pulses to sound an alarm, stop the sweep, and read out the accumulated     
     
     
        number. .Iadd. 16.  A system as defined by claim 15, wherein, c. said transmitter means comprises an oscillator adapted for frequency modulation over a band of frequencies,   d. said receiving means comprise filter means selective of said band, a detector, and a low-pass circuit,   e. said resonant frequencies are uniformly spaced within said band, and   f. said multiplexing means comprise a linear modulator for advancing the frequency of said oscillator regularly from one end of said band to the other slowly enough to excite in each of said resonators an unambiguous response..Iaddend. .Iadd. 17. A system as defined by claim 16,   g. wherein said resonators are quartz crystals..Iaddend..Iadd. 18. A system as defined by claim 16,   g. wherein said transmit-receive isolation means comprise, i. a switch having a first and a second state, connected to said transmitter means, said receiving means, and said transmission line, arranged so that in its first state energy passes freely between said transmitter means and said transmission line and is substantially barred from passing from said transmission line and from said transmitter means through said receiver means, and in its second state signals pass freely between said receiver means and said transmission line,   ii. together with driving means for periodically oscillating said switch between its said two states at intervals which are substantially briefer than the ringing time of said resonators, and substantially longer than the response time of said filter means..Iaddend..Iadd. 19. A system as defined by claim 17,     h. wherein said transmit-receive isolation means comprise, i. a switch having a first and a second state, connected to said transmitter means, said receiving means, and said transmission line, arranged so that in its first state energy passes freely between said transmitter means and said transmission line and is substantially barred from passing from said transmission line and from said transmitter means through said receiver means, and in its second state signals pass freely between said receiver means and said transmission line,   ii. together with driving means for periodically oscillating said switch between its said two states at intervals which are substantially briefer than the ringing time of said resonators, and substantially longer than the response time of said filter means..Iaddend..Iadd. 20. A system as defined by claim 19, wherein,     i. said ringing time is of the order of one-tenth second,   j. said response time is of the order of one-tenth of a millisecond,   k. said switching intervals are of the order of 10 milliseconds, and wherein   l. said oscillator frequency is advanced from one of said resonant frequencies to the next in the order of one second,   m. whereby a complete scanning cycle is completed in the order of one minute..Iaddend..Iadd. 21. A system as defined by claim 19, wherein,   i. said ringing time is more than 10 milliseconds,   j. said response time is less than one-tenth of a millisecond,   k. said switching intervals are between two and 50 milliseconds, and wherein   l. said oscillator frequency is advanced from one of said resonant   
     
     
        frequencies to the next in less than one second..Iaddend..Iadd. 22.  A system as defined by claim 19, wherein said oscillator is a voltage-controlled oscillator..Iaddend. .Iadd. 23. A detection system for remote detection of the presence in or absence from a transmission line of any of a plurality of resonators, each of said resonators being connectable with and disconnectable from said transmission line, the combination of, a. a plurality of crystal resonators, each of said resonators being resonant at a frequency which is one of an ordered set of frequencies and different from the resonant frequency of the others of said plurality, each of said resonators when connected with said transmission line being set to ringing by application of a voltage at said one frequency to said transmission line, and   b. an alarm set remote from said resonators connected to said transmission line, said alarm comprising, i. transmitter means including a variable controlled oscillator for generating sequential electrical signals having substantial energy components at each of the resonant frequencies of said plurality of resonators,   ii. receiving means connected to said transmission line for detecting signals at each of said resonant frequencies,   iii. transmit-receive isolation means for connecting said transmitter means to said transmission line so that the energy components at said resonant frequencies generated by said transmitter means flow into said transmission line and are substantially prevented from flowing directly into said receiving means,   iv. multiplexing means for rendering said receiving means sensitive to said resonant frequencies according to a predetermined program of intervals and order,   v. alarm means connected to said receiver means responsive to a departure from said program, and   vi. counting means connected to said multiplexing means for counting signals corresponding to each detected resonant frequency..Iaddend. .Iadd.     
     
     
        4.  The invention defined in claim 23, wherein said variable controlled oscillator comprises frequency synthesizer means programmed to switch from frequency to frequency of said crystal resonators in accordance with a predetermined pattern..Iaddend.