How Do You Know if You're Using a Smart Phone to Monitor Your Kids?

In about a year, i'm saying to my kids, you know, if you're careful, you can bike to school. And when i do do that, i'm going to want them to take a phone with them. It doesn't have to be a smart phone, but something that says, like, here's where they are and they can text you r call you at any time. So i guess that's kind of, with their consent and with their knowledge. I'm not like chipping them in their sleep and they don't know that. But once they get on the inner net, it becomes a question if,. you know, do i limit them completely? Do i