There have been several different Bunker Hill alarm-type devices from HARBOR FREIGHT mentioned in these threads before (a driveway motion sensor for when someone approaches and those two-part window alarms which will sound when one part detaches from the other). Today I saw these Vibration Alarms while in the store. 2 for $4.99. They use a button-type battery. When it detects a jolt or enough motion to set it off, it sends out a 90 dB siren alarm within 2 seconds. The alarm will auto turn off in 25 seconds. There is an On/Off switch. Strap it on your prop where it won't be noticed and turn it on. Should send panic into anyone who decides to pick your prop up.