After reading what I wrote I don't think I described it correctly. Think of this way, (just example) I have a child who I'm taking to the mall I stop to talk to someone and the child see something and wander away before I even had change to notice. Once the child is say 10 feet away from me the device (size of beeper) starts to play a noise to tell me that child is no longer close to me (like leash with no leash). I was thinking the device would just have to send a signal out to see/hear the other device which it then does nothing, if don