The BRK 9120B is a hard-wired smoke alarm with audible battery backup. It features a dual ionization smoke sensing chamber, 85dB alarm, 9V battery backup, and a "silence" feature. This alarm features a "Smart Technology" system that is designed to reduce nuisance alarms, 

Features

• LED power-on indicator
• "Latching Alarm Indication" remembers which unit initiated an alarm
• 85dB solid state T3 piezo horn
• "Smart Technology" reduces nuisance alarms
• Single Test/Silence button eliminates confusion
• Ionization technology best for flaming fires
• 9V battery back-up for audible alarm 
  
• Quick, easy (hard-wired) installation 
• Available with or without a strobe light

Specs

• Hard-wired installation
  
• Meets UL Standard 217
• Designed for single-family homes
• Side-load battery drawer allows easy replacement
• Battery backup for sound alarm only
• 9V battery backup for audible alarm 
• Ten-year manufacturer's warranty

Documentation