Lauren has a medical alert bracelet that has all of her information on it should she get lost. If someone takes her that is another story. We have alarms on our house that tell us what door has opened and they ding really loud. She is 12 but has been a wonderer all of her life.
We also have alarms on all our door and even his bedroom window. We have lost him once, never want that to happen again. He has also been a wonderer all his life, as soon as he could walk he would escape, and fast too. What I am looking for is a proximity alarm so that if he gets lets past a certain distance that has been program on the bracelet it beeps on your device and lets you know. It would be great on vacation and especially at school. Even though he has his own EA he can still manage to escape. Should have named him Houdini.
Another thing to look into is the devices that police departments sometimes have which allows searching with a special device they have in case of wandering. I would use it in addition to one that notifies you, just in case he wanders further than you can track. The police department here has one that can even search underground a ways or in buildings.