Power sources

Battery-powered alarms are easier to install than plug-in or wired models. What's more, they will continue to work during a power failure. Most smoke alarms require annual battery replacement and give a warning beep when the battery is low. There are some models that use a lithium battery, which should last the life of the smoke alarm. CO alarms typically require annual battery replacement as well. In all cases, follow the manufacturers instructions provided with your alarm for choosing the correct replacement battery and its replacement schedule.

Hardwired smoke alarms operate on household 120-volt AC power and connect directly to a dedicated electric box typically found on the ceiling. Most can be interconnected with other alarms, which is an advantage. (Interconnecting involves wiring alarms together, which is typically done as an integral part of the home's wiring during construction.) Some come with backup battery power, which you must replace annually.

Plug-in CO alarms plug into a standard 120-volt electrical outlet, just like a lamp or clock radio. Because of their accessibility, you can test and reset them easily without a ladder or chair. Those models are available with backup battery power.

Interconnecting smoke alarms, joined either by using smoke alarms designed to be wired together or linked wirelessly, set off all the alarms in your home when any one goes off. That would allow your family the best chance to hear or be awakened by an alarm sounding anywhere in your home. Many building codes have required new homes to be constructed with wiring in place to power and interconnect smoke alarms placed on every floor and in every bedroom for 15 or more years. If you live in one of those homes, choose a replacement alarm designed to work in this system. If you live in a home without such wiring, there are now alarms designed to interconnect wirelessly.

A few wireless smoke alarms have a feature allowing them to interconnect into a hardwired alarm system. That can be useful to add alarms in the home without having to call in an electrician. To be safest, if your interconnected alarms don't have dual sensors (photoelectric and ionization smoke sensors), be sure that the system incorporates some alarms with each type of sensor.

Manufacturers have yet to develop a battery-powered device that operates both types of sensors and uses wireless technology to interconnect alarms, according to a maker we spoke with. An obstacle is that such a setup would drain the batteries. But you can interconnect dual-sensor devices that operate through the AC power in your home, such as some models from Kidde.

Note that you can incorporate some smoke and CO detectors into an overall home-security system. Depending on your system configuration, the alarm can be heard inside and outside the house and the monitoring service can notify police or fire departments or even call your cell phone.

Interconnecting CO alarms can be accomplished even though most CO alarms available today are not intended to be interconnected. Some wireless smoke alarms are available with an integral CO alarm. That can allow the CO alarm to set off other interconnected devices to ensure the warning is heard.