MPT1320 Licence exempt walkie talkies as used by bikers etc. Scanner to listen to the frequency also licence exempt. PCL circuitry recognises a specific series of clicks. In the case of ours it is 5 clicks in a specific timing.
Never fired up by interference nor failed to fire up. We can assign any frequency that the scanner can 'hear' this includes air and ground bands.
But the MPT licence exempt is the best way to go for those looking for an excuse to find illegality in use. It is also more reliable than an SMS. We don't get a mobile service in the air around our place, in fact we barely get one on the ground......