If your family sleeps with bedrooms doors closed, it's especially important to install detectors inside the bedrooms. Be sure you can hear detectors from each bedroom. Most smoke detectors can be installed easily. Most operate either on batteries or household current. A detector that plugs into a wall outlet must have a restraining device so that the plug cannot accidentally be pulled from the wall.
Detectors can also be hard-wired into the electrical system.
But never hard-wire a detector to a circuit that can be turned off at a wall switch. Because smoke rises, each detector should be mounted high on a wall or on the ceiling to detect the first traces of smoke. For a wall-mounted unit, the top of the detector should be 4 to 12 inches from the ceiling. In a room with a high pitched ceiling, mount the detector on or near the ceiling's highest point. Most home fires start in living areas - the den, family room or living room.