Person testing alarm

What kind of smoke alarm (smoke detector) should I buy?

Smoke alarms are important to fire safety in your home because, the risk of dying in home structure fires is 55 percent lower in homes with working smoke alarms than in homes with no alarms or none that worked. Buying smoke alarms can be a bit confusing to someone who is not aware of all the different types and the terminology being used. Because of this, I am going to break down some of the most frequently asked questions to help you choose the best alarm.

I want to note that there is a difference between a smoke “detector” and a smoke “alarm”, basically a smoke detector is just a sensor that monitors for smoke and is connected to a whole building fire alarm system, while a smoke alarm has both the sensor to monitor for smoke and the speaker that emits the sound to notify the home occupants.

What are the different types of smoke alarms?

Having the proper number of working smoke alarms installed (regardless of the type) in the correct locations is key when it comes to safety.

Ionization vs Photoelectric

There are some different types of alarms that can be purchased that have different pros and cons. The first difference you will see is Photoelectric vs Ionization. The difference between the two types is the sensor that is used to detect the smoke. An ionization smoke alarm is generally more responsive to flaming fires (imagine a fire where you can see the flame), and a photoelectric smoke alarm is generally more responsive to smoking smoldering fires (such as a cigarette).


Ionization smoke alarms utilize a small amount of radioactive material to ionize air molecules into positively and negatively charged molecules that create a small electric current. The introduction of smoke into that ionized air will reduce the amount of current and cause the smoke alarm to sound. Typically, smoke alarms with Ionization detectors tend to be less expensive than alarms with photoelectric detectors.



Photoelectric smoke alarms utilize a light source and a photosensitive cell. When smoke enters the chamber, light scatters and is picked up by the photosensitive cell, causing the alarm to sound.



Combination Ionization and Photoelectric

To get an alarm that is just as responsive to smoldering fires as it is to flaming fires, you can get an alarm that has dual sensors. These alarms have both an ionization sensor and a photoelectric sensor that will cause the alarm to sound. A dual sensor alarm provides the best protection and for that reason it is recommended.  

Intelligent multicriteria alarms

There are alarms available that are multicriteria or intelligent alarms, what this means is they use many different sensors such as photoelectric, ionization, and heat along with an algorithm to detect a fire. Because of the multiple sensors, this type of alarm is better at reducing unwanted, or "nuisance” alarms from non-fire sources (such as when you are cooking), it does not necessarily mean that the alarm is able to detect fires sooner.

Voice smoke alarms

There are some smoke alarms available that will produce both the temporal 3 pattern (a continued set of three loud beeps -- beep, beep, beep) as well as having a voice announcement that can tell you things like where the smoke is being detected or if there is an issue with the smoke alarm.

What is a combination smoke and Carbon Monoxide (CO) alarm?

A combination smoke carbon monoxide alarm is an alarm that has both sensors to sense smoke and to sense for carbon monoxide. These alarms may look like smoke alarms and are mounted on the ceiling or the wall near the ceiling. If your house has fuel burning equipment (oil or gas boiler, oil or gas furnace, oil or gas water heater, fire-place ect.) then you will need to also have carbon monoxide detection within your house.

How do smoke alarms get their power?

There are many ways that smoke alarms can get their power.

Replaceable batteries

Some smoke alarms will get all their power from batteries that are replaceable, they can be a 9v battery, AAA battery, AA battery, or another type of battery. These batteries should be replaced at least once a year and the alarm tested every month.

10-year battery alarms

Some smoke alarms come with a sealed non-replaceable battery that can provide power to the smoke alarm for up to 10 years. This alarm does not require the batteries to be replaced, however, you should still be testing them monthly.

Hardwired with battery backup

Some smoke alarms are provided with both primary power that is hardwired in from the home’s electrical system and a secondary battery backup. The secondary battery backup can be either a battery that needs to be replaced at least yearly, or it can be a 10-year sealed battery that does not need to be replaced.

Do I need battery or hard-wired smoke alarms?

If your home has hard wired connections, then you should replace the alarms with hard wired smoke alarms of the same manufacturer. You can use a different manufacturer; however, this may require an electrician to come in and wire in a different plug (also see the interconnection section below).

If you are performing renovations or building a new home, check with the local building department and/or fire department for code requirements.

How often do I need to replace my smoke alarms?

Smoke alarms must be replaced:

  • Every 10 years based on date of manufacturer on the back label (7 years for Combination CO/Smoke Alarm)
  • if the alarm sounds an end-of-life signal (see back of alarm for description of signal)
  • if the alarm fails a monthly operability test
  • or, after a fire event

How do I know I am buying a quality alarm I can rely on?

Smoke alarms are required to be tested by a third party recognized laboratory to stringent product standards. Make sure that the alarm you are buying was tested by and labeled (shown on packaging and on the label of the alarm) by a recognized testing laboratory. Some examples include Underwriters Laboratories (UL) and Intertek.


What are interconnected smoke alarms, and do I need them?

Smoke alarm interconnection means that the alarms are connected so that if one alarm sounds, all the alarms in the home  will sound. Interconnected smoke alarms are more likely to alert occupants of a fire anywhere in the building. Because of this, new building, fire, and life safety codes will require smoke alarms in new buildings or remodeled buildings to be interconnected.

Typically, if you are just replacing an alarm, then you can replace them with the same type that was there, if they are currently interconnected then you need to replace with interconnected, if they are not interconnected, you are not required to install interconnected alarms, however, interconnected alarms will provide an additional level of safety. It is especially important to have interconnected smoke alarms, if you sleep with doors closed.


You can get smoke alarms that are interconnected with a wire or that are wireless. If your smoke alarms are hard-wired look to see if there are three wires coming from the alarm, if they are all connected, then it is likely the alarms are interconnected. If the smoke alarms are not hard-wired, then you will need to look on the alarm to see if it is capable of being wirelessly interconnected. You can also just press the test button on one alarm and listen to see if the other alarms in the house go off, if they do then you have interconnected smoke alarms.


When interconnected smoke alarms are installed, it is important that all the alarms are from the same manufacturer or are listed as compatible (see manufactures instructions for compatible alarms). If the alarms are not compatible, they may not sound.

In what rooms do I install smoke alarms?

Check your local building, fire, or life safety codes for your specific requirements, you can call your local fire prevention department as well. But in general smoke alarms need to be installed:

  • Inside each bedroom, outside each sleeping area (such as in the hallway) and on every level of the home, including the basement.
  • On levels without bedrooms, install alarms in the living room (or den or family room) or near the stairway to the upper level, or in both locations.
  • Smoke alarms installed in the basement should be installed on the ceiling at the bottom of the stairs leading to the next level.
  • Larger homes may require additional smoke alarms

Do I install the alarm on the ceiling or the wall? 

Mount smoke alarms high on walls or ceilings (remember, smoke rises). Wall-mounted alarms should be installed not more than 12 inches (300 mm) away from the ceiling (to the top of the alarm). 

If you have ceilings that are pitched, install the alarm within 36 inches (910 mm) of the peak but not within the apex of the peak (4 inches (100 mm) down from the peak).

Avoid installing the smoke alarms in places where there is air movement or drafts such as near windows or near the air supply from an HVAC system.



How do I reduce unwanted alarms?

If you are required to place a smoke alarm near cooking appliances or the door to a bathroom based on the arrangement of your house, there are some things to keep in mind to reduce any unwanted alarms.     

To limit the amount of unwanted alarms from cooking, you should place your alarm at least 20 feet (6.1 m) from the cooking appliance. If the alarm is a photo-electric type, has a silencing button, or is listed for a resistance to common cooking smoke then you can place it as close as 10 feet (3.0m) away from the cooking appliance.

If placing a smoke alarm in the hallway near the door to the bathroom with a shower in it, you should place it at least 36 inches (910 mm) from the door to reduce the impact of steam from the shower on the alarm.

What if someone in my home is deaf or hard of hearing?

There are smoke alarms and alert devices that alert people who are deaf or hard of hearing. These devices include strobe lights that flash to alert people when the smoke alarm sounds. Pillow or bed shakers designed to work with your smoke alarm also can be purchased and installed.

Learn more

If you would like to learn more about smoke alarms or carbon monoxide alarms, check out our public education smoke alarm page, Carbon Monoxide alarm page, or Chapter 29 of NFPA 72®, National Fire Alarm and Signaling Code®.


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Shawn Mahoney
Technical Services Engineer with a masters degree and PE in fire protection supporting subjects throughout the association

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