Donna D's photo of a sticker regarding a motion detector gave me an idea. Perhaps a good deterrent would be to have a motion sensor or accelerometer turn on a loud siren/horn. A person could have a hidden switch somewhere to arm/disarm the system. The entire thing should have its own backup battery
so the system would work if the thieves cut the tongue battery
. Better yet, detect that the tongue battery
has been disconnected and have the siren go off in case the thieves were just after the battery.