Is there a date rape drug detector ?

YES!

http://www.ia.ucsb.edu/93106/2004/June7/rape.html

But I don't think it's something you can carry in your purse and test your cocktail before drinking on a first date. 

I would suggest that if you think you were raped, go to a medical professional immediately and get tested. It's a simple procedure where they take a blood sample and check the vaginal area.

For future reference, always keep your drink with and never put it down at a bar. If you do put it down, don't drink anymore of it. Just get another one and keep it next to you at all times. This is a classic way that guys who are trying to drug you can get away with it. They find an unsuspecting girl who has put her drink down for a minute and slip the odorless, tasteless drug into their drinks. So don't let this happen to you.

I just came across this - I think this one can go in your purse:

http://www.drinkspikedetector.com/ 

Yes it's called common sense. Don't let a man bring you a drink at a bar, if you leave your drink don't finish it. You should order another one and  at house parties have a group to watch your back and if you start acting out of character or pass out have them there to take you home not anybody else. If you are at  a house party by yourself with people you don't know have a few drinks before you get there and forgo  their hospitality  and don't trust women you don't know cause your sisters can be just as twisted as any man out there.