No experience, but how about infrared? This would pick up body / engine heat and trigger. Just don't know about false alarms, but would seem to be OK if mounted in the right places. ----- Original Message ---- From: "scottebulger@comcast.net" scottebulger@comcast.net Bob Austin advised he used an alarm system on his boats. I'm wondering what kind of an alarm would be effective on a a boat. If the goal is to sound an alarm prior to them getting on board, I'm not aware of technology that will acheive this on a boat? If I alarm the windows and doors, I don't see the value, because at that point they are on board.