Where to install a smoke detector and its positioning are as important as having this life saving device installed at all. Placing a smoke detector in a wrong location might delay its response to smoke or even prevent it from sounding an alarm at all.
Although, you should install smoke alarms by following device manufacturers guidelines, and the NFPA standards (National Fire Protection Association), your local jurisdiction might have a different idea. This idea is usually LESS smoke detectors - Chicago is one of the examples.
Since it is your life we are talking about, following just a minimum requirement is not enough - for literally a few dollars more, you can get maximum protection.
Proper Placement of a smoke alarm based on IRC (International Residential Code), IBC (International Building Code) and NFPA:
New construction:
Smoke detectors must be hard wired (power supply from the electrical panel) and require battery backup. Your jurisdiction might require a dedicated circuit for this purpose - if such isn't required, make sure that you smoke detector hasn't been installed on a circuit / tapped to the wall switch controlled ceiling light fixture or outlet receptacle. Putting a smoke alarm on a GFCI protected electrical circuit also isn't a good idea.
Do not use rechargeable type batteries for smoke detectors, good quality alkaline type battery is the right choice. Smoke alarms shall emit a signal when the batteries are low - replace the battery with a new one as soon as you hear that repeating sound.
Smoke detectors are required in each sleeping area and adjoining bedroom. Like I've mentioned before, some jurisdictions require less - Chicago is one of the examples where smoke detectors are not required inside the bedroom / sleeping area. Instead, you have to install a smoke alarm within 15' from the bedroom entrance. In larger homes / apartments, where bedrooms are located more than 30' apart, two or more smoke detectors might have to be installed.
At least one is required on each story of the house and in the basement. Crawlspaces and uninhabitable attics do not require a smoke detector installation. However, in case your attic or crawlspace contains a furnace, water heater, or any appliance that could become a source of fire (gas, oil, electric), have a smoke alarm installed as well (required by some jurisdictions and highly recommended if not required).
Smoke detectors must be interconnected - one triggered smoke detector activates all of them. Not all types of smoke alarms have the "interconnection" feature, which is extremely important - smoke developing in one section of the house would activate the closest device and automatically all of them at the same time.
Existing construction:
While remodeling, hard wiring and interconnection of smoke detectors is not required if finishes would have to be removed. However, you can still achieve maximum protection by using an interconnected wireless smoke alarm system.
The smoke alarm shall be clearly audible in all bedrooms over the background noise levels with all intervening doors closed. That's why regular testing of the smoke detector siren is so important - just like any mechanical / electronic device - sometimes they fail.
Enclosed interior staircases also require a smoke detector, and one shall be installed on the ceiling of the top floor. Staircases act like chimneys and smoke rising from the lower floor would activate the device giving you an early warning.
Smoke detector placement - rules apply to all of the locations described above.
This is extremely important and at the same time quite simple, unfortunately very often done completely wrong. It's probably because we don't like to read the manuals and often assume that we know what we're doing.
When installing a smoke alarm on the ceiling (preferable location / might be required in some jurisdictions), place it as close to the center as possible, never closer than 4" (10cm) to the sidewall or corner.
If for any reason, ceiling installation is not practical and wall installations are permitted, you can install smoke alarms on the wall with its top edge at a minimum of 4" (10cm) and a maximum of 12" (30.5cm) below the ceiling.
Before placing a smoke detector on the ceiling or wall, consider checking the house insulation. Older homes might be missing a ceiling (if open to the attic) or exterior wall insulation. This would allow extreme heat or cold transfer from exterior into the house, creating a thermal barrier, and prevent smoke from reaching / activating the alarm. If this is the case (you can simply touch the wall or ceiling during very hot or cold days), mount a smoke detector on an interior wall of the house.
Install smoke detectors in rooms with cathedral, sloped, peaked, gable ceilings at or within 3' from the highest point (measured horizontally).
Install smoke detectors in each section of the room / area that has been divided by a partial wall. The wall might be coming down from the ceiling (at least 24") or up from the floor.
Install smoke alarms on a tray-shaped ceiling (also called coffered ceiling) on the highest portion of the ceiling or on the sloped portion of the ceiling within 12" (30.5cm) vertically down from the highest point.
DO NOT install smoke detectors in following areas to minimize possibility of false alarms:
Areas where combustion particles are present (Combustion Particles - the by-products of burning process)
garages
poorly ventilated kitchens
close to furnaces and water heaters - I wouldn't agree with this one, because presence of those particles would be a sign of combustion process problems
If you decided to have one installed in those areas, photoelectric type smoke alarm might be less annoying.
Damp or very humid areas such as bathrooms. The humidity levels after taking a hot shower could result in a false alarm.
Within 3' from the forced air heating and / or cooling system air supply vents, in a direct airflow area, close to the whole house fan locations. High air flow could blow smoke or shift it away from the detector preventing it from responding properly or at all.
Near fluorescent lights, where electronic "noise" may cause nuisance alarms.
Dusty areas, where particles of dust could cause smoke alarm failure or false alarm
In areas where air temperature may fall below 40°F (4°C) or rise above 100°F (38°C)
Avoid areas near the doors and windows while installing a smoke alarm
If you got that far, I hope you have more than a general idea on where to install smoke detectors in your house, and what is the optimal smoke alarm placement.
