The BRK First Alert CO5120BN is a hard-wired T4 carbon monoxide alarm with battery backup. Hard wired for installation by a licensed electrician. T4 alarm pattern with loud 85 decibel alarm. Reduced nuisance alarms with Intelligent Sensing Technology. Interconnectable with up to 18 BRK alarms. Battery backup for audible alarm. The BRK First Alert CO5120BN is a hard-wired carbon monoxide combo alarm with battery backup. It features a CO sensor, Intelligent Sensing Technology? for fewer unwanted alarms, an 85dB horn, 9V battery backup, side-load battery drawer, two silence features and is interconnectable with up to 18 devices. Applications include residential and institutional applications including hospitals, hotels, motels, dormitories and other multi-family dwellings. The Intelligent Sensing Technology" system is designed to reduce nuisance alarms. The "Latching Alarm Indication" remembers which unit initiated an alarm. When interconnected, the unit that triggered the alarm rapidly flashes its red LED indicator. After the alarm condition subsides, the initiating unit will store in memory or "latch" the information and begin to flash the red LED indicator once every 5 seconds. The "Smart Interconnect" feature allows the unit to be interconnected to other BRK CO and smoke alarms. If there is a smoke event, the interconnected CO5120BN horn pattern will emit the T4 alarm sound, the same sound as a smoke alarm (4 beeps, pause, 4 beeps). If there is a CO event, the interconnected CO alarms will sound with their normal horn pattern. Battery installation and removal can occur while the unit is mounted via the side load battery compartment. Features: Latching alarm indicator remembers which unit initiated an alarm Intelligent Sensing Technology reduces nuisance alarms 85dB horn T4 sound pattern Smart Interconnect is interconnectable to both BRK smoke and CO alarms Two silence features can silence the low battery chirp up to 8 hours or temporarily silence and unwanted alarm Quick, easy installation Feature Details Brand First Alert Mfg part # 5268511 UPC 029054856173 Warranty Seven year limited warranty Weight (lbs) 0.57 Battery operated? Yes (batteries optional) Batteries included? Yes Battery details (1) 9V Alkaline Country of Manufacture Mexico System (no system / stand-alone) Alert Type(s) Vibration Flashing Light Loud Audible Low Vision / Deaf-Blind No No Yes No Transmitter / Receiver Transmitter Alert Trigger(s) Baby Cry Carbon Monoxide Mobile / Smartphone Doorbell / door knock Motion Pager / SOS Phone / VP Smoke / Fire Sound Severe Weather No Yes No No No No No No No No Expandable Yes Portable No Battery backup Yes USB charger No