I have 5 daughters - well 1 is in college now so I guess I can't track her
but the others would be nice as they get older.
think of the accessories Voodo, start with a bracelet, but then you can do like necklaces, shirts (if washing would be ok ), ankle bracelets, etc, etc You tell your kids they have to wear this or that device for thier safety but you will give them a choice on some cool things to wear...
If this could take off you could brand the "M & M (singer or candy) I'm safe bracelet", etc