BRK / First Alert SC9120B Hardwired Smoke & Combination Carbon Monoxide with Battery Backup

The BRK SC9120 hardwire combination smoke and CO alarm with battery backup includes these features: Quick plug-in power connector for easy installation. 120-volt AC inter-connectable (with maximum 18 compatible devices). The alarm can be interconnected with up to 12 other compatible smoke alarms and six compatible devices like bells, horns, repeaters and door closers. If one unit triggers an alarm, all smoke alarms in the series will sound. Power indicators show which unit in the series initiated the alarm. Ionization sensor which is more effective at detecting flaming fires which consume combustible materials rapidly and spread quickly. Microprocessor controlled for fewer nuisance alarms. Single test/silence button which both silences a non-threatening alarm or low battery warning and allows you to test the unit's functionality. Automatically performs internal test of functionality. Latching alarm indicator which automatically identifies which unit initiated the alarm. Separate smoke and carbon monoxide visual and audible warnings. Battery drawer lock and mounting bracket lock for tamper resistance. AC power indicator and alarm indicator light. Low battery warning "chirp" and missing battery tab. 9-volt battery backup for peace of mind during power outages.