How to Test Smoke and CO Detectors

Battery Replacement Best Practices

• Use name-brand batteries: Buy fresh 9-volt or AA batteries from a reputable brand. Off-brand or dollar-store batteries may have shorter lifespans and inconsistent voltage output. Check your detector's manual for the correct battery type—using the wrong size or type can prevent the unit from functioning.
• Replace all at once: Even if some batteries tested fine, replace them all during your annual check. This ensures every detector starts the year with full power and eliminates the guesswork of trying to remember which ones were swapped last.
• Note sealed-battery units: Some newer detectors use sealed 10-year lithium batteries that cannot be replaced. When the battery dies, you replace the entire unit. If you have these, you still need to test them annually and check the expiration date on the back.
• Dispose of old batteries properly: Don't throw 9-volt batteries in the trash loose—the terminals can short against metal objects and cause fires. Tape the terminals with electrical tape before disposal, or take them to a battery recycling drop-off point.

• Vacuum the exterior vents: Use a vacuum cleaner with a soft brush attachment to gently clean the vents and openings around the detector body. This removes dust and cobwebs that can block smoke from entering the sensing chamber. Avoid using compressed air, which can push debris deeper into the unit and damage sensitive components.
• Wipe the housing: Use a lightly damp cloth to wipe down the exterior of each detector. Don't spray cleaning products directly on the unit or submerge it in water. Chemical residues from sprays can coat the sensor and cause false alarms or reduced sensitivity.
• Verify ceiling placement: Detectors should be mounted on the ceiling or high on a wall, no more than 12 inches from the ceiling. Keep them at least four inches from corners where dead air pockets can delay smoke reaching the sensor. In rooms with peaked or cathedral ceilings, mount the detector within three feet of the peak but not at the very top.
• Check required locations: Your home should have smoke detectors inside every bedroom, in the hallway outside each sleeping area, and on every level including the basement. CO detectors are required on every level and near sleeping areas. If you're missing coverage in any of these locations, add detectors now—most building codes require this minimum coverage.

• Interconnected (hardwired): When one detector senses smoke or CO, every detector in the house alarms simultaneously. This ensures you hear the alarm regardless of which floor or room you're in. Most homes built after 1993 are required to have interconnected detectors. If one unit in an interconnected system fails, it can sometimes disable the chain—another reason to test each unit individually.
• Wireless interconnected: If your home doesn't have hardwired detector circuits, wireless interconnected detectors communicate by radio frequency. When one triggers, it sends a signal to all other compatible units. These are an excellent upgrade option for older homes that only have standalone battery-powered detectors, without the cost of running new wiring.
• Standalone (battery only): Each detector operates independently. A smoke detector in the basement will alarm, but the detector in your upstairs bedroom will not. In a two-story home, this means a fire that starts on a lower floor may not wake you until smoke physically reaches your bedroom detector. If you have standalone units, strongly consider upgrading to wireless interconnected models—they're typically $25 to $40 each and install in minutes.