Indicator showing when consumer goods are out of recommended date - changes colour in dependence on time and temp.

摘要

The indicator uses a coloured dot (4) to indicate when consumer goods (e.g. milk) have become unusable. The dot changes colour and the colour is a function of time and temp. Alternatively, instead of chaging colour, the dot's electrical resistance may change. An ohmmeter is then needed to measure this resistance. The dot can be incorporated into a range of goods, e.g. ice cream, photographic films, medicine, ink inside a printer etc.