There's an Indiegogo campaign for cups, stirrers, and straws which change color if a drink contains one of the three most common date rape drugs. This would be a great thing, but they're only trying to raise $50,000.
They've already got a compound which changes color, but my feeling is that putting it into a dye and getting the dye to stick to plastic and making sure the stuff is safe and then going into even small scale reproduction is not a $50,000 project. On the other hand, I don't know the state of the art.
If you think the project is sound, they've got $13,500 to go and only 64 hours left.
Link thanks to filkertom.
Fast cheap chemical analysis is a tech I've been looking forward to for some time. My handy example is drinking water. Why does Philly water make my tongue sting about half the time?
Admittedly, testing tap water for all the dubious things which might be in it-- or even the top twenty dubious things-- is a harder project.