Smoke and CO Detector Wiring Inspection

Per NFPA 72 and UL 217/UL 2034, smoke detectors are required on every level of the home, inside each bedroom, and outside each sleeping area. CO detectors are required on every level and near each fuel-burning appliance or attached garage. Hardwired detectors with battery backup are required in new construction and major renovations.

1. Verify local code requirements for smoke and CO detector placement

2. Confirm detectors are required to be hardwired (not battery-only) for the project scope

3. Check if combination smoke/CO detectors are permitted by local code

4. Verify photoelectric vs ionization requirements (some jurisdictions require photoelectric)

5. Confirm compliance with any additional local amendments beyond the base code

6. Check expiration date requirements — smoke detectors typically must be replaced every 10 years

- Battery-only detectors installed where hardwired are required by code

- Missing detectors on one or more floors

- No CO detectors installed despite fuel-burning appliances being present

- Detectors past their expiration date (10-year lifespan for smoke detectors)

Per NFPA 72 and UL 217/UL 2034, smoke detectors must be installed inside every bedroom, outside each separate sleeping area within 300 mm (12 inches) of bedroom doors, and on every level including basements. CO detectors are required outside sleeping areas on every level, in rooms with fuel-burning appliances, and in or near attached garages.

1. Verify a smoke detector is planned for inside each bedroom

2. Confirm smoke detectors outside each separate sleeping area

3. Check for smoke detector on every level including basement and finished attic

4. Verify CO detector placement on every level with sleeping areas

5. Confirm CO detector near attached garage and fuel-burning appliances

6. Check that detector locations avoid dead air spaces (corners where walls meet ceiling)

- Missing detector in one or more bedrooms

- No detector in basement or finished attic

- CO detector missing near attached garage

- Detector planned for dead air space near peak of cathedral ceiling

Per NEC (NFPA 70) and NFPA 72 and UL 217/UL 2034, hardwired smoke and CO detectors must be connected to a reliable power source. They may be on a dedicated circuit or share a general lighting circuit (not a switched circuit). The wiring must include an interconnect conductor (typically a 3-conductor cable: 14/3 with ground) so all units alarm simultaneously.

1. Verify power source is an unswitched circuit (not controlled by a wall switch or GFCI/AFCI that could be tripped)

2. Confirm wiring uses 14/3 with ground (or 14/2 with separate interconnect wire per manufacturer)

3. Check that the circuit breaker is properly sized and labeled in the panel

4. Verify wiring method complies with local code (NM-B cable, conduit, etc.)

5. Confirm adequate cable length and routing between all interconnected units

6. Check for proper junction boxes at each detector location

- Detectors wired to a switched circuit (power interrupted when switch is off)

- Only 14/2 cable used without interconnect conductor

- Circuit shared with high-draw appliance causing voltage fluctuations

- Wiring run without junction boxes at intermediate connection points

Per NFPA 72 and UL 217/UL 2034, ceiling mounting is preferred for both smoke and CO detectors. If wall-mounted, the top of the detector must be 100 mm (4 inches) to 300 mm (12 inches) from the ceiling. Detectors must be at least 300 mm (12 inches) from any corner where walls and ceiling meet. Keep detectors away from air vents, windows, doors, and cooking appliances.

1. Verify ceiling mounting is used wherever possible

2. If wall-mounted, check detector is 100 mm (4 inches) to 300 mm from ceiling

3. Confirm detector is at least 300 mm (12 inches) from any wall-ceiling corner

4. Check that detector is at least 3 m (10 feet) from cooking appliances to avoid nuisance alarms

5. Verify detector is not near air supply vents, ceiling fans, or windows

6. Confirm mounting bracket is secure and detector snaps firmly into place

- Detector installed in dead air space at wall-ceiling junction

- Detector too close to kitchen, causing frequent nuisance alarms

- Detector near air vent, preventing smoke from reaching sensor

- Detector mounted on sloped ceiling at the wrong position (should be within 900mm of peak)

Per NFPA 72 and UL 217/UL 2034, all smoke and CO detectors within a dwelling unit must be interconnected so that activation of any one detector causes all detectors to alarm. This can be achieved through hardwired interconnect (third wire) or wireless interconnect modules for compatible detectors.

1. Verify all detectors are interconnected (hardwired or wireless)

2. Test interconnection — trigger one detector and confirm all others alarm

3. If using wireless interconnect, verify all units are properly paired

4. Check that interconnect wire is not shared between separate dwelling units

5. Confirm maximum number of interconnected units does not exceed manufacturer limit (typically 12-24)

6. Verify that smoke and CO detectors produce distinct alarm patterns (3 beeps for smoke, 4 beeps for CO)

- Detectors not interconnected — only local alarm sounds

- Wireless interconnect units not properly paired after installation

- Interconnect wire accidentally shared between adjacent apartments

- All detectors sound the same pattern (cannot distinguish smoke from CO)

Per NFPA 72 and UL 217/UL 2034, all hardwired smoke and CO detectors must have battery backup to ensure operation during power outages. Sealed 10-year lithium batteries are preferred for maintenance-free operation. Replaceable batteries (AA or 9V) require regular replacement. All detectors must provide a low battery alert.

1. Verify each detector has a battery installed and functional

2. Check battery type — sealed 10-year lithium preferred, replaceable AA/9V acceptable

3. Test battery backup by disconnecting power and verifying detector still functions

4. Confirm low battery alert chirp is audible from sleeping areas

5. For replaceable batteries, verify fresh batteries are installed at commissioning

6. Label each detector with installation date and battery replacement date

- Battery missing or dead in one or more detectors

- Low battery chirp not audible from bedrooms with doors closed

- Sealed battery detector with expired 10-year lifespan

- Replaceable batteries not installed during commissioning

Per NFPA 72 and UL 217/UL 2034 and manufacturer instructions, all detectors must be tested after installation using the test button and, for smoke detectors, with approved smoke test spray. Testing must verify both local and interconnected alarm operation. All installation details must be documented.

1. Press test button on each detector — verify alarm sounds locally

2. Test interconnection — trigger one detector and verify all others alarm

3. Use smoke test spray on each smoke detector to verify sensor response

4. Test CO detectors with test button (gas testing typically not required at commissioning)

5. Verify all alarm patterns are correct (3 beeps smoke, 4 beeps CO per NFPA)

6. Document: installation date, detector model/serial, battery type, test results

7. Provide homeowner with documentation and maintenance schedule

- Only test button used — smoke sensor not actually tested

- Interconnection not verified during testing

- No documentation provided to homeowner

- Detectors not tested after final finishing (paint or drywall dust can impair sensors)