I think this is pretty cool...
If you're worried about someone making off with your kids (as has happened in several high profile cases lately and has happened to my husband when he was a kid), here's a way that you can find them again. The main unit costs $400 and there's several service plans running from $25-$35/month. They're not just cool for parents. Kids can use them as beepers as well (therefore, cool for kids).