2 3/4" overall. Personal alarm featuring a siren to maximize attention to yourself when needed for self defense. The compact design allows defendme to be easily carried on a keyring, purse, backpack, etc. 120 dB siren. 30 consecutive minutes total duration. Stand-by-time is up to six months. Be prepared in case of aggression, take defendme wherever you go. It is recommended to carry the personal alarm when walking or running alone, entering isolated buildings, hallways, elevators, parking lots, public restrooms, dark places, etc.