Replace a Smoke / CO Detector
NFPA recommends replacing smoke detectors every 10 years and CO detectors every 5–7 — sensors degrade even if the unit still chirps. The "chirp every minute" usually means low battery; the chirp every 30 seconds + red light usually means end-of-life.
Tools
- ✓
- ✓
Materials
- +Combo smoke+CO units (e.g., Kidde or First Alert) cover both with one device. Use 10-year sealed-battery units to skip future battery changes.
Steps
-
1
Twist off the old unit
Most detectors are bayonet-mounted: rotate counterclockwise ~15° to release it from the ceiling plate.
-
2
Disconnect the harness (hardwired only)
Squeeze the plastic connector tab and pull the power harness out of the back of the old unit.
-
3
Check the mounting plate compatibility
Same brand replacement = old plate usually fits. Different brand = swap the plate (3 ceiling screws).
-
4
Connect the new unit and mount
Plug the harness into the new unit, twist onto the plate clockwise until it locks. Write the install date on the back of the unit in marker.
-
5
Test
Press and hold the test button until you hear the full alarm cycle (≥5 seconds). Restore breaker if hardwired.