Smart Interconnect-Interconnects up to 24 Kidde devices (of which 18 can be initiating), Battery Backup (2-AA batteries included)-Provides protection during power outages.Front Loading Battery Door-Replace the backup batteries without disconnecting from mounting bracket Humidity range:10%-95% relative humidity, non-condensing.Battery Lockout System-The battery door will not close unless the batteries are properly installed, Alarm Tamper Resist-Helps deter from tampering and theft, Adjustable Mounting Bracket-Makes installation fast and easy. Works with existing smoke and combination smoke and CO mounting brackets. Peak Level Memory-Announces ?CARBON MONOXIDE PREVIOUSLY DETECTED? if alarm has detected a CO level of 100ppm or higher since it was last reset, HushTM Feature-Silences nuisance alarms for approximately 9 minutes. (Smoke must be present before HushTM is activated) Ionization Sensor Technology-Ideal for detecting fast flaming and other types of fires, est Button Functions:? Tests the unit for proper operation - Peak Level memory - Resets the Carbon Monoxide alarm Green LED-Illuminates to indicate the unit is receiving AC power. Flashes once every 60 seconds to indicate battery only mode. Flashes once per second during alarm to indicate initiating alarm. Flashes once every 16 seconds to indicate smoke or CO previously detected. Flashes every 2 seconds while the alarm is in HUSHTM mode Voice Alert Intelligent sensor technology Front load battery door Alarm tamper resist Peak level memory