• Install smoke alarms on every level of your home, including the basement, making sure that there is an alarm outside every separate sleeping area. New homes are required to have a smoke alarm in every sleeping room and all smoke alarms must be interconnected.
• Hard-wired smoke alarms operate on your household electrical current. They can be interconnected so that every alarm sounds regardless of the fire's location. This is an advantage in early warning, because it gives occupants extra time to escape if they are in one part of the home and a fire breaks out in another part. Alarms that are hard-wired should have battery backups in case of a power outage, and should be installed by a qualified electrician.
• If you sleep with bedroom doors closed, have a qualified electrician install interconnected smoke alarms in each room so that when one alarm sounds, they all sound.
• If you, or someone in your home is deaf or hard of hearing, consider installing an alarm that combines flashing lights, vibration and/or sound.
• Mount smoke alarms high on walls or ceilings (remember, smoke rises). Ceiling mounted alarms should be installed at least four inches away from the nearest wall; wall-mounted alarms should be installed four to 12 inches away from the ceiling.
• If you have ceilings that are pitched, install the alarm near the ceiling's highest point.
• Don't install smoke alarms near windows, doors, or ducts where drafts might interfere with their operation.
• Never paint smoke alarms. Paint, stickers, or other decorations could keep the alarms from working.

Sensing Systems

Most smoke alarms use one of two common sensing systems for detecting a fire.

• Ionization-type smoke alarms have a small amount of radioactive material between two electrically charged plates, which ionizes the air and causes current to flow between the plates. When smoke enters the chamber, it disrupts the flow of ions, thus reducing the flow of current and activating the alarm.
• Photoelectric-type alarms aim a light source into a sensing chamber at an angle away from the sensor. Smoke enters the chamber, reflecting light onto the light sensor; triggering the alarm.
• Ionization smoke detection is generally more responsive to flaming fires and photoelectric smoke detection is generally more responsive to smoldering fires. Both types of technologies have improved home fire safety.

Source: NFPA's "U.S. Experience with Smoke Alarms and Other Fire Detection/Alarm Equipment" report by Marty Ahrens, April 2007.