Kidde CO120X - Carbon Monoxide Relay Module - Activates Auxiliary Warning Devices - For Use with Kidde CO Alarms by Kidde The Kidde CO120X can be used to activate auxiliary warning devices such as external bells and sirens, hallway or stairway lighting. This relay will only activate when it receives a CO signal from an interconnect Carbon Monoxide Alarm. When in the activated mode (as a result of a CO signal), this device will deactivate if it receives a smoke interconnect signal from a compatible device.