With the ID15 you get 2 door stopper alarms.  Simply place one of the alarms 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. These door stopper alarms come 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 these lightweight units in your luggage.  The on / off switch will prevent them from accidentally sounding.  This alarm requires two (2) AA batteries that are not included.  They measure 6 inches x 1 and seven-eighth inches x 1 and five-eighth inches.  For a single pack of this alarm please see item ID14 or for a door stop alarm with an adjustable movement sensor and streetwise security packaging please see item SDS85.