Does the device constantly broadcast something so you can see when people are in range? Can this be turned off? What if I don't want to announce everyone where

Does the device constantly broadcast something so you can see when people are in range? Can this be turned off? What if I don't want to announce everyone where I am? (yeah, it probably doesn't send GPS constantly, but constant radio signals are pretty easy to triangulate). I would just want to broadcast a message and then all devices within range should pick it up and see if they can decrypt it (i.e. was it meant for them)