By sounding an alarm and alerting you to a fire in time to escape, an inexpensive household smoke alarm can cut your chances of dying in a residential fire in half. Smoke detectors, also known as smoke alarms, save so many lives, that 39 states have laws requiring them in private homes.

There are dozens of brands of smoke alarms for sale in hardware, department, and discount stores. Be certain that the smoke alarm you buy bears the label of approval from an independent testing laboratory.

Several types of alarms are available. Some run on batteries; others run on household current. Some detect smoke using an "ionization" sensor; others use a "photoelectric" system. All labeled smoke alarms, regardless of power source or sensor type, will offer adequate protection provided the unit is properly installed and maintained.

According to the Standard on Household Fire Warning Equipment (NFPA 74), minimum protection requires a smoke alarm outside each sleeping area and on every level of the home (including the basement). On floors without bedrooms, alarms should be installed in or near living areas - dens, living rooms, or family rooms.

Be sure everyone sleeping in your home can hear your smoke alarms even with bedroom doors closed. If not, or if any residents are hearing impaired, install additional alarms inside bedrooms. There are smoke alarms for the hearing impaired on the market. These units flash a light in addition to sounding an alarm.

For extra protection, NFPA suggests installing alarms in dining rooms, furnace rooms, utility rooms, and hallways. Smoke alarms are not recommended for kitchens, bathrooms, or garages, where cooking fumes, steam, or exhaust could set off false alarms, or for attics and other unheated spaces, where humidity and temperature changes might affect a alarms' operation.

Because smoke rises, mount alarms high on a wall or on the ceiling. Wall mounted units should be mounted 4 to 12 inches from the ceiling, and a ceiling mounted unit should be positioned at least 4 inches from the nearest wall. In rooms with high, pitched ceilings, mount the alarm at or near the ceiling's highest point.

In open stairways (no doors at the top or bottom), position smoke alarms anywhere in the path of smoke moving up the stairs. But always position smoke alarms at the bottom of closed stairways, such as those leading to the basement, because dead air trapped near the door at the top of a stairway could prevent smoke from reaching the alarms smoke sensor.

Don't install a smoke alarm too near a window, door, or forced air register where drafts could interfere with the unit's operation.

Most battery powered smoke alarms, as well as units that plug into wall outlets, can be installed using only a drill and a screwdriver by following the manufacturer's directions. Plug-in alarms should be installed with appropriate restraining devices to prevent them from being accidentally disconnected from their outlets. Alarms can also be hard-wired into a building's electrical system. Never connect a smoke alarm to a circuit that can be turned off at a wall switch.

Following manufacturers instructions, test your smoke alarm weekly and replace batteries at least twice a year. Many battery powered units "chirp" or give some other audible signal when their battery power is low. Resist the temptation to borrow smoke alarm batteries for other uses.

Clean your smoke alarms according to the manufacturers instructions at least once a year. Dust and cobwebs can reduce an alarms sensitivity to smoke

NEVER PAINT A SMOKE ALARM