Simply place the alarm behind any door. If an intruder attempts to open the door, the wedge-shaped design will prevent it from opening and activate a 100 dB alarm, scaring off the would-be intruder and alerting you to the attempted entry. This Door Stopper Alarm Set of 2 Set of 2 comes with a movement sensor. If anyone attempts to move the unit the alarm will immediately activate. (There is a 10 second delay before the movement sensor activates). When traveling, just toss this lightweight unit in your luggage. The on / off switch will prevent it from accidentally sounding. This alarm requires two (2) AA batteries that are not included. The door stop measures 6 inches x 1 and seven-eighth inches x 1 and five-eighth inches.