Photoelectric smoke alarms use a beam of light to detect smoke.  They are more responsive to fires that begin with long period of smoldering.  Photoelectric smoke alarms tend to be less prone to nuisance alarms in your kitchen.

Ionization smoke alarms detect fire by sensing changes in heat and air quality in your home.  They are more responsive to flaming fires, but are more susceptible to nuisance alarms due to cooking.  Ionization smoke alarms are characterized by a small radiation symbol on the back.

Hard-wired smoke alarms are powered directly by your home’s electricity. Hard-wired smoke alarms will not function in the event of a power outage, so make sure your alarms have a battery back-up feature, or install additional battery-operated smoke alarms. 

If you are replacing a hard-wired smoke alarm, you must replace it with another hard-wired unit.  You cannot substitute a battery operated smoke alarm in its place.

Battery operated smoke alarms get their power from batteries. Batteries must be replaced when the low-battery indicator chirps, when the smoke alarm doesn’t function properly when tested, or every 6 months.

Smoke alarms are now available with 10 year lithium batteries which never need to be replaced for the life of the unit. These smoke alarms are great for hard to reach places and those who have difficulty maintaining their smoke alarms.

Interconnected smoke alarms communicate with each other so when one smoke alarm detects fire they all sound.  These smoke alarms provide your family with the highest level of early warning in the event of fire.  If you have more than one hard-wired smoke alarm in your home, they should already be interconnected. 

Interconnected smoke alarms can also be installed in homes that aren’t already wired for it.  Wireless smoke alarms are battery operated alarms which still communicate with each other with wireless signals.  These alarms can also be great for detection in a nearby building such as a garage or shed.  Modern ‘smart’ alarms also have the ability to be wirelessly interconnected, even when they are only battery operated.

Some smoke alarms are combination units which detect carbon monoxide as well as smoke and fire.  Combination alarms are available in hard-wired and battery operated models, and have two different alarm sounds to tell you whether its smoke or CO.  In newer homes a combination may be required to meet Code requirements.

Smoke alarms are available with strobe lights, pillow/bed shakers, and other notifiers for those who are haring or visually impaired.  ‘Smart’ alarms also send a notification to a smartphone or other device that would alert someone who otherwise is unlikely to hear an alarm.