Okay... Criminals know about the GPS tracking devices, especially those in the human trafficking business and other organized crime. They throw the phone away, or even destroy it. This isn't just "what Michael would do if he kidnapped someone," it's common knowledge in the "less than reputable businesses." Some of the more tech-savvy criminals (yet again, those in organized crime) actually use these tracking devices against people. So they know where your children are too. I'm not trying to scare anyone. I'm just trying to make people more aware of how criminals work.

And, teenagers need freedom and trust from their parents. It's a part of the development process for them to make their own choices and become more independent. You can say, "I'm only doing it to protect you," but they usually don't perceive it that way. When they are denied that freedom and trust, they will rebel. And when they rebel, they run right into the hands of those you're trying to protect them from.