Smoke and CO Detector Installation and Maintenance

Detector Types

Ionization detectors respond fastest to fast-flaming fires like burning paper or grease. Photoelectric detectors respond faster to slow, smoldering fires like a cigarette on a couch cushion. Dual-sensor units contain both technologies. The NFPA recommends either using both types or using dual-sensor units throughout the home.

Carbon monoxide detectors are a separate device, though combination smoke/CO units exist. CO detectors are required in homes with fuel-burning appliances (gas furnace, gas water heater, gas stove, fireplace, attached garage). Place them on every level and outside sleeping areas. CO is roughly the same density as air, so they can go at any height, though manufacturers typically recommend 5 feet above the floor.

Placement Rules

Smoke detectors go on the ceiling or high on a wall (within 12 inches of the ceiling). Place one inside every bedroom, one outside each sleeping area (in the hallway), and at least one on every level of the home, including the basement. In two-story homes, put one at the top and bottom of each stairway.

Keep detectors away from windows, doors, and HVAC registers where drafts could delay smoke detection. Stay at least 10 feet from cooking appliances to reduce false alarms. In rooms with peaked or cathedral ceilings, mount the detector within 3 feet of the peak but not at the very apex, where dead air can prevent smoke from reaching the sensor.

Installation Tools

You need a drill or screwdriver, the mounting bracket that comes with each detector, appropriate anchors for your ceiling material (drywall anchors for drywall, toggle bolts for plaster), a pencil for marking holes, and a step ladder. That's it. Each unit takes about 10 minutes to mount.

For hardwired interconnected systems, you also need a voltage tester to confirm the circuit is off before working, wire strippers, wire nuts, and basic wiring knowledge. Hardwired detectors connect to a dedicated circuit and communicate with each other so that when one detects smoke, all units alarm. Many newer wireless detectors offer the same interconnection without the wiring.

Interconnection

Interconnected detectors are vastly safer than standalone units. When a detector in the basement triggers, every detector in the house alarms simultaneously, giving people on the second floor time to escape before smoke reaches them. Hardwired interconnection uses a third wire between units on a shared circuit.

Wireless interconnection uses radio frequency communication between compatible units. This is the practical choice for retrofit in existing homes where running new wire between detector locations would mean opening walls and ceilings. Most major brands offer wireless interconnection within their product line, but units from different manufacturers typically won't communicate with each other.

Maintenance and Replacement

Test every detector monthly by pressing the test button. Replace batteries annually, or when the low-battery chirp starts. Detectors with sealed 10-year lithium batteries eliminate the annual battery change but still need monthly testing. Vacuum or blow out detectors every 6 months to remove dust that can cause false alarms or reduce sensitivity.

Replace the entire detector unit every 10 years regardless of whether it seems to be working. The sensors degrade over time and become less reliable. There's a manufacture date on the back of every unit. If you don't know when yours were made and can't find the date, replace them. A pack of detectors costs less than dinner out and the installation takes an afternoon.

Frequently Asked Questions