Environment dependent - temperature independent color changing label

Abstract

A timing device comprises a sensing material and/or a component which is sensitive to the presence of an environmental attribute. The environmental attribute drives and speeds up or slows the timing device as the concentration of the attribute increases or decreases, respectively. Alternatively, the timing device is activated upon sensing the presence of the environmental attribute and indicates a total passage of time from exposure/activation of the timing device. Particularly, sensing materials of varying types are able to be used to indicate exposure to a variety of substances. For example, in some embodiments, the timing device comprises a sensing material which is sensitive to the presence of ultraviolet radiation. Alternatively, the sensing material is sensitive to other variables such as x-ray radiation and nuclear radiation. In further embodiments, the sensing material is sensitive to biological or physical contamination.

1 - 22 . (canceled) 
     
     
         23 . A timing device for indicating an exposure to an environmental attribute, comprising:
 a. one or more reactive zones, the one or more reactive zones configured to change color at a different time after being activated and being geometrically arranged to collectively indicate a total exposure to the environmental attribute, wherein the timing device is activated upon initial exposure to the environmental attribute.   
     
     
         24 . The timing device of  claim 23 , wherein a portion of the reactive zones comprises a photosensitive medium that as developed changes color. 
     
     
         25 . The timing device of  claim 23 , wherein a portion of the reactive zones comprise a diffusion layer and a dye that migrates through the diffusion layer to change color. 
     
     
         26 . The timing device of  claim 23 , wherein a portion of the reactive zones comprises an electro-chemical material that is reduced or oxidized to change color. 
     
     
         27 . The timing device of  claim 23 , wherein a rate of color change of the one or more reactive zones is directly related to a concentration of the environmental attribute. 
     
     
         28 . The timing device of  claim 23 , wherein the total exposure is a range of time. 
     
     
         29 . A system for monitoring a level of exposure to an environmental attribute, comprising:
 a. a timing device for indicating an exposure to the environmental attribute; and   b. an external holder for holding the timing device that comprises an attachment mechanism for attaching the system to an additional article.