Designed to activate an auxiliary device like a bell siren strobe light exhaust fan alarm panel or door closer when alarm is sounded. Now works with "Smart Interconnect" BRK CO alarms. The RM4 has form-C contacts that once connected to BRK 120volt AC alarms automatically activate whenever the alarm sounds and will automatically deactivate when the alarm shuts off. Meets UL 317 UL2034 and UL539 for accessories.