BRK Model CO250LBT is a state of the art carbon monoxide alarm designed to provide early warning of the presence of carbon monoxide. It features an electrochemical carbon monoxide sensor, an 85dB horn, a full function test switch and a red LED light that indicates DC power or alarm. The CO250LBT features a 9VLithium battery that will power the alarm for at least 5 years. It also features tamper proof mounting bracket that prevents removal of the alarm from the wall or ceiling using a tamper proof spanner screw. A tamper proof spanner screwdriver bit is also included. It also features a tamper resistant locking pin that locks alarm cover to prevent removal of battery when tamper proof bracket is removed. This alarm has two silence features. Low Battery Silence: Temporarily silence the low battery chirp for up to eight hours. Alarm Silence: Silence alarm for several minutes. Perfect for apartment, dormitory or hotel applications. The compact, low profile design complements any decor. When voltage drops to a pre-set warning level, the horn will "chirp" approximately once per minute to indicate a fresh battery is needed. To insure the battery is always replaced properly, the cover is designed to resist closing when the battery is missing.