If the intention is merely to open up the conversation, why not get a fake SCRAM bracelet? http://www.amazon.com/Costume-Accessory-Detention-Arrest-Bracelet/dp/B00A122EX8
It would have the same effect ('What's on your ankle?') without the unnecessary costs associated. Personally, I don't see the point, but honestly... kids are weird and if it isn't hurting her then it should be OK. (really, I would see teenagers intentionally trying to set off a bracelet like this)