Smaller Than a Pack of Cigarettes yet produces 130 DB of sonic blast energy. Deter an attacker, or summon help when you need it. Also acts as a portable door alarm -- mount to your door at home, or in a hotel or dorm room, and the alarm will sound if the door is opened! Size is 2-7/8" x 2-1/8" x 1", weight is 2 oz without 9V battery (not included).