How to Add a Monitored Smoke or CO Detector to an Alarm Panel

Why this matters

A monitored smoke or carbon monoxide detector is often the most valuable device on a residential alarm, because it calls for help when nobody is home or when everyone inside is asleep or already overcome. It is also the device where a wiring shortcut or a wrong zone type has the worst outcome: a detector that loses power without telling anyone, a CO alarm the station reads as a burglary, a fire signal that sends police instead of the fire department. This card adds one properly: a listed device, a supervised circuit, the right zone type, and a test that proves the station receives FIRE and CO as what they are.

First: whose job is this

Fire alarm work is separately licensed in many states and localities, and the license that covers burglary installation often does not cover it. Some jurisdictions also require a permit and an inspection for any fire detection connected to a monitored panel, even in a house. Before quoting, confirm the shop holds what the jurisdiction requires for fire and for CO; if it does not, this device goes to a licensed fire alarm contractor and the customer is told so in writing. The license line and how combination panels sit across it are owned by Combination Fire and Burglary Panels and the License Line, and the licensing landscape by Alarm and Low-Voltage Licensing Varies by State and City.

Also first: what this does not replace

A monitored detector added to an alarm panel does not remove, replace or monitor the house's existing smoke alarms unless the whole system was designed and approved as the household fire alarm system under the code your jurisdiction has adopted. Leave existing smoke alarms in place and working. Where the detector goes on the ceiling follows NFPA 72, in the edition your authority having jurisdiction has adopted, and the detector maker's instructions; placement rules are not taught here.

Step 1: choose a device the panel is listed to use

Three ways to add one, each with its own compatibility rule:

• Wireless smoke, CO or combination detector from the family the panel's receiver supports. Simplest in a finished house. Fire and CO wireless devices carry stricter supervision requirements than burglary devices, and the panel must support them.
• Two-wire smoke detector, powered from the zone loop itself. Only on a panel zone listed for two-wire smokes, and only with detectors whose compatibility identifier the panel's documentation lists. A two-wire detector not on that list may never alarm, or may never reset.
• Four-wire smoke detector, with a signaling pair plus a separate power pair from the panel's resettable power output. Works on most panels with a fire-capable zone. The method this card wires.

For CO, use a detector listed for connection to a control panel (system detectors carry a listing to UL 2075), not a plug-in or battery single-station CO alarm with a relay bolted on.

Step 2: put the account on test, including fire and CO

Tell the station you will be sending fire and CO signals and ask how they handle a test: some stations also need the fire department notified, and some jurisdictions require it. Put the account on test for every signal type, per How to Put an Alarm Account on Test and Take It Off. A fire signal that reaches a station not expecting it starts a fire department response.

Step 3: run the cable

A four-wire smoke loop needs four conductors: two for signaling, two for power. Use the cable type the NEC, Article 760 as adopted by your jurisdiction, requires for power-limited fire alarm circuits in that location; which run gets which cable is owned by Alarm Cable Types and Which Run Gets Which.

Getting wire to a ceiling in a finished house usually means the attic. Before crawling or fishing through attic insulation, identify it. Loose-fill vermiculite and unknown loose fill can contain asbestos; do not disturb it, and do not fish wire through it. Route another way or stop and have it tested. Drilling ceiling plaster or paint in a home built before 1978 can release lead dust: drill with a shroud and vacuum, or under the shop's lead-safe work practices, and do not dry sweep the dust.

Step 4: wire it supervised, with nothing unsupervised anywhere

The governing rule for a supervised loop is that every conductor runs into and out of each device, with no T-taps and no branches, and the supervision device is at the far end. Here is the loop on this job, a new fire zone 3 with two four-wire smoke detectors:

SIGNALING LOOP, ZONE 3 (FIRE)
PANEL Z3 + ---+---------+----RELAY CONTACT---+
              |         |    (closed while   |
            DET 1     DET 2   coil powered)  EOL
            alarm     alarm                  |
            contact   contact                |
              |         |                    |
PANEL Z3 - ---+---------+--------------------+

RESETTABLE POWER, SUPERVISED BY THE RELAY COIL
PANEL RES + ---DET 1 in/out---DET 2 in/out---RELAY +
PANEL RES - ---DET 1 in/out---DET 2 in/out---RELAY -

Each + on the loop is a detector terminal with the
wire landed in and out, not a splice.

How each condition shows at the panel:

• Normal. Power is on, so the relay coil is energized and its contact is closed. The panel sees the end-of-line resistor through the loop.
• Alarm. A detector's alarm contact closes across the loop, which the fire zone reads as an alarm.
• Broken power wire anywhere, or power lost. Because power runs into and out of each detector to the relay at the end, a break at any point de-energizes the coil, the relay contact opens, and the loop reads open: trouble. Without the relay, a detector could lose power and the zone would still read normal, which is a smoke detector that has silently stopped working.
• Broken signaling wire. The loop reads open: trouble.

The end-of-line resistor value is per the panel's documentation, and it sits at the last device, after the relay, never at the panel. The supervision logic itself is owned by End-of-Line Resistor Supervision: Open, Short and Normal.

Why resettable power: a four-wire smoke detector latches in alarm and stays latched until its power is interrupted. The panel's resettable output drops power briefly when the alarm is cleared at the keypad, which resets the detectors. A detector fed from constant auxiliary power stays in alarm until someone pulls a wire.

Step 5: add the wireless CO and check the power budget

On this job the CO detector went in as a wireless system CO detector in the upstairs hall outside the bedrooms, location per its maker's instructions, enrolled to the panel's receiver and confirmed for signal at its mounting spot per How to Enroll a Wireless Sensor and Confirm Its Signal.

The two smoke detectors and the relay coil add standby and alarm current to the panel's resettable output, which has its own rating in the panel manual, and to the panel's total load. And a panel carrying fire detection usually has to meet the fire secondary-power duration of NFPA 72 as adopted, commonly 24 hours of standby plus an alarm period, rather than whatever burglary duration the battery was sized for. Rerun the worksheet per How to Size a Standby Battery for an Alarm Panel. On this job the existing 7 Ah battery still covered the fire duration with the added load; on a heavier system it would not have.

Step 6: program the zone types

• Zone 3: fire. A 24-hour fire zone type, which reports as a fire alarm whether armed or not, typically sounds the temporal-three evacuation pattern on the sirens, and drives the resettable power reset.
• The CO detector: a CO zone type, distinct from fire, so the station receives a CO alarm and follows the CO response, and the sirens sound the temporal-four pattern used for CO where the panel supports it.

Never program a smoke or CO detector as a burglary or generic 24-hour zone. The station dispatches on the signal type it receives.

Step 7: test it, from device to station

With the account on test:

1. Supervision. Lift the end-of-line resistor at the last device: the keypad shows a zone 3 trouble. Restore it. Then lift the resettable power positive at the relay coil: the relay drops and the keypad again shows a zone 3 trouble. Restore it. Both troubles should reach the station.
2. Smoke. Test each detector with the listed test aerosol its maker specifies, from a ladder with someone footing it. The keypad shows a fire alarm on zone 3, and the station receives FIRE, zone 3, with the right description. Clear it at the keypad and confirm the detectors reset.
3. CO. Use the test the CO detector's maker specifies. On many detectors the test button tests the sounder and electronics, not the sensor; the maker says whether a sensor test needs test gas. Confirm the station receives CO, not fire and not burglary.

On this job the station read back, in order: zone 3 trouble, restore; zone 3 trouble, restore; fire alarm zone 3 smoke (upstairs hall detector); reset; fire alarm zone 3 smoke again (basement detector, tested separately, because one conventional zone cannot tell the station which detector tripped); CO alarm zone 25 upstairs hall CO; and the restorals.

Step 8: close out

Confirm with the station that every signal arrived as the right type, that the fire and CO response plans and contacts on the account are current, and that the account is back to normal before you leave. Leave the customer the detector's maker instructions, show them what the keypad displays for fire, CO and trouble, and note on the record the installed date and the replace-by date the detector's maker states; both smoke and CO sensors have a service life.

References

• NFPA 72, National Fire Alarm and Signaling Code, in the edition adopted by your authority having jurisdiction: detector placement, secondary power, testing.
• NFPA 70 (NEC), Article 760 as adopted by your jurisdiction: power-limited fire alarm circuit cabling.
• UL 2075, Gas and Vapor Detectors and Sensors: listing for system-connected CO detectors.
• See related: Combination Fire and Burglary Panels and the License Line
• See related: End-of-Line Resistor Supervision: Open, Short and Normal