
Or just use your nose. And avoid prawn or egg mayo sandwiches in general, especially from train stations.
Packaging giant Bemis and Norway's ThinFilm will print sticky labels capable of monitoring and remembering the conditions in which their attached goods have been stored. The labels will be developed from ThinFilm's printed memory and PARC's printed transistors (which are licensed exclusively to ThinFilm). Bemis will fund the …
FYI: The lemons and potatoes used in those childhood Science experiments were not what was generating the electric charge-- the purpose that they served was to be the ion bridge between the anode and the cathode that you were using. It is the electrochemical reaction between the metals used for the anode and cathode that actually produces the electrical potential difference (the voltage of the lemon or potato "battery").
Source: http://en.wikipedia.org/wiki/Lemon_battery
There was a similar announcment some years ago: a simple steel ball inside ice filled transparent plastic capsule visible from the outside.
It was extremely cheap, but retailers and manufactures plainly refused to use it, as it would expose the bad practices they normally use: shutting off for the night freezers, etc.
And ... *ahem*Sainsbury's*ahem*
I don't know what freezing-thawing-storage regime my local store uses but it's almost impossible to buy potatoes that don't turn green or bread that doesn't go stale within a day or two and well before its use by date. The state of their meat products at times has made me consider vegetarianism.
The idea is fine but unlikely to catch on IMO as it's not in the supermarkets' collective interests and they'll use the argument of extra cost to ensure consumers don't support the idea. The economy is too tight to let them add monitoring labels and sneak on an extra bit of profit as well where they'd no doubt argue it as a good idea.