Review on Mengshen Wireless Bicycle Alarm: Anti-Theft Burglar Security Alarm for Bike, Motorcycle, Car, Vehicles, Door, Window - 113db Super Loud & Waterproof (Includes Remote Control) by Steven Stager

I used them to secure a moving Penske truck when parked overnight. I would stick one in every truck door. You stick it in the door, close and lock the door, and then set the alarm from outside with the remote control. I left the default value (highest). Just like touching the doorknob on the outside of the truck activates the alarm. The alarm doesn't go off right away, it emits some sort of warning tone to let you know it's on you. If you continue what you are doing, the alarm will sound. However, it's not loud enough to wake you up in a hotel room, but I was hoping it would be loud enough to scare off anyone trying to sneak in. Now that I've never heard of anything going off and our truck not being broken into, I don't know if the alarm actually went off and scared someone away, or if no one tried to break in at all. All in all these alarms were just one aspect of all the measures I took to keep the truck safe and these alarms definitely gave me some extra peace of mind at night.