Plan carbon monoxide alarm placement and count.
Carbon monoxide alarm counts come from coverage rules rather than from area. The baseline in NFPA 720 and most residential codes is one alarm outside each separate sleeping area and one on every storey of the home, including the basement. Two extras are worth adding where the risk is concentrated: one near the door to an attached garage, because a car started with the door open is a common source, and one in or adjacent to the room holding the boiler, furnace or gas water heater. Unlike smoke, CO has almost the same density as air and mixes through the room, so mounting height matters far less than being close enough to hear the alarm while asleep. Alarms have a sealed lifespan — usually 7 to 10 years from the date on the back — and stop being protective when that expires even though the test button still beeps.
Carbon Monoxide Alarm Check
Alarms = one per storey + one outside each sleeping area + 1 if attached garage + 1 if any fuel-burning appliance
Carbon monoxide is lethal and this figure is planning guidance, not a code compliance check. Follow your local building code, the alarm manufacturer's instructions and NFPA 720, and have fuel-burning appliances serviced annually by a qualified technician.
Any height that meets the manufacturer's instructions. CO is close to the density of air and mixes, so unlike smoke alarms there is no ceiling requirement — audibility from the bedrooms matters more.
Yes. The electrochemical sensor degrades whether or not it has ever seen CO, and most units are stamped with a 7 to 10 year replace-by date. The test button checks the horn and battery, not the sensor.
It can, provided it is sited where both need coverage. Just note that smoke alarms want ceiling mounting near bedrooms, which is a valid CO position too, so combination units usually work well outside sleeping areas.