110VAC Smoke Detector Integration (with timer)

Most new contruction or remodeled homes have 110VAC interconnected smoke detectors incorporated into the design. The building code requires smoke detectors in each sleeping area and on each level hallways.

The detectors can be tied into a conventional alarm system by use of a special relay (i.e. Firex 499). The relay activates when the detector trips and sends 110VAC to the other detectors sounders. There are two weaknesses to the relay.

  • The relay only activates if there is 110VAC present. The danger is that if a fire has caused the 110VAC to fail the relay will not activate.
  • Power spikes or brief smoke detector malfunctions can cause the relay to momentarily trip. I have had experience with people turning on vacuum cleaners putting a spike on the line that trips the relay.

To avoid the first problem I usually put one wireless smoke detector at the highest point  programmed directly into the alarm panel. This will detect smoke as a back-up if the 110VAC is not functional.

For the power spike problem I install a relay (i.e. Altronix 6062) in the 110VAC smoke detector relay circuit to require a smoke detector to be tripped for 20+ seconds before it will trigger the alarm panel.  The alarm panel I use in my example is a Honeywell Vista20P (see diagram)


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