This is a recurring question I have every time I go to a public toilet. Why not having a smart plastic that test your urine for drug traces right on the spot instead of that stupid advertisement ? The ad reads "Say no to drugs".

1) it would actually be useful by "informally" reminding people of their actions/status,
2) the results don't need to be 100% accurate -no legal issue there
3) no privacy issue either -urinoirs are separated, the body blocks most of it and one ususally tends not to look at the neighbor's.

Okay, drugs might not be the best example since traces remains in the body weeks after consumption.

The problem remains the same, why don't designers (me included) go/push for the whole nine yards when it is so obvious and useful ?