Universal Security Instruments CD-9385 120-Volt AC Wired-In 3-LED Interconnectable Carbon Monoxide Alarm Interconnect up to 18 units, 12 smoke alarms maximum; when one alarm goes off all units sound their alarm the 120 VAC direct plug in offers fast and easy installation The alarm sounds with its loud 85 decibel horn and the red LED indicator flashes. A green LED light indicates AC power The mounting plate attaches to the junction box and covers drywall cutouts for easy installation A yellow LED indicator flashes with any fault conditions