There's actually several of these kind of devices on the market, I've seen different watches, cell phones and even a backpack. They have their place, I have 3 kids all under the age of 10 and kids that age can get lost very easily if you don't keep a close eye on them. I've put serious consideration into buying some kind of GPS tracker for my kids.
It's important to realise, however that a kid is going to get abducted even if they are wearing some wizzbang locater device if they're not first taught how to defend themselves. There's no substitute for teaching your kids the most important lesson of all: Stay away from strangers! I've taught my kids some very important things, that all parents should teach them:
- Don't approach strangers
- If one approaches you, run
- If the worst happens and someone grabs you, make a huge fuss - kick and scream, do what ever you can to draw attention.
Right now, I'm investing my $250 not into a GPS device but into taking my kids to self defense classes. Much apart from the fact it's great exercise and teaches them discipline and respect, it may save their lives one day. Plus, they're having a lot of fun doing it :)