A proprietary radio signal joins multiple alarms together so that when one alarm sounds, they all sound. Wire-free or hardwire interconnect triggers each connected alarm in the network to sound once smoke or CO is detected, which can provide more time to react to a hazard. The National Fire Alarm and Signaling Code (NFPA 72) has required smoke alarms in new homes to be interconnected since 1989, which traditionally involves running wiring to each alarm. Older and remodeled homes can now be updated to current standards without having to run new interconnect wiring to each alarm (AC power wiring still required).