Two birds with one stone time again…
I am always surprised by how much good stuff gets thrown away. Contact lenses are a case in point. They aren’t all that cheap, yet we jetison them daily in the interests of convenience and health.
A wonderful invention in themselves, soft ones also have the property that they flatten out when left to dry. This suggests a possible way to re-purpose the technology.
If a lens is placed in a container whose dryness requires only crude monitoring, a simple light beam shone through the lens can be made to focus on some kind of cheap photodetector. As the local atmosphere dries, the lens flattens and the light will be refracted much less, causing the photodetector to receive fewer photons.
Perhaps (sterilised) lenses could be used in this way to monitor the environment within large numbers of eg individual food packages.