Types of CO and smoke detectors: Do you know the difference?

By Allstate

Last updated: October 2023

You change the batteries in your smoke detectors twice a year, and test them every month. But do you know what type of smoke detectors you have? Or, that having one kind over another may make a difference? Or, if they can detect carbon monoxide (CO)?

There are two main smoke detector types, and each has a sensor that detects smoke and fire differently, depending on the origin of the fire. You can purchase each kind of smoke detector or get a dual sensor smoke detector that combines the two methods of detection. Also, some smoke detectors have a CO detector, but you’ll need to check the text on the inside of your alarm to see if it does.

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What is an ionization smoke detector?

The first smoke detector type, ionization, has alarms that are generally more responsive to a flaming fire (for instance, when a lit candle tips over and ignites a curtain), according to the National Fire Protection Association (NFPA). These alarms use "ions," or electrically charged particles, to help detect smoke in the air.

What is a photoelectric smoke detector?

The second type of smoke detector, photoelectric, uses a light beam to help detect the presence of smoke. According to NFPA, these alarm types are more effective at sounding when a fire originates from a smoldering source, like a lit cigarette that falls into a couch cushion. Smoldering fires may fill a home with dangerous gases before a fire ever erupts.

What is a dual sensor smoke detector?

Dual sensor smoke detectors use both ionization and photelectric sensors for improved fire detection, according to the NFPA. Ionization sensors are sensitive to flaming fires, while photoelectric sensors respond more to fires that build over a period of time. Combined into one device, they offer a greater breadth of protection.

What is a carbon monoxide/CO detector?

A carbon monoxide detector alerts you if carbon monoxide is present in your home or building, SafeWise explains. Carbon monoxide is known as the “silent killer.” It’s invisible to the naked eye, can’t be seen or tasted. Sources of carbon monoxide include common household appliances – stoves, furnaces, water heaters, etc.

For these reasons, it’s crucial to install a carbon monoxide detector, adds SafeWise, as they continuously monitor the air for dangerous levels of carbon monoxide, and alert you of any possible hazards. You can also get a smoke detector that has a CO detector in it.

Is there a difference between a CO detector and a CO alarm?

CO detectors give you a continuous display of carbon monoxide levels in your home, while CO alarms alert you only if those levels become dangerous, according to Emergency Plan Guide. There are also devices that combine the two.

What is a smart smoke detector?

Smart smoke detectors can alert you of smoke, and even dangerous CO levels, via a smartphone app, according to the New York Times. They can detect and warn you if the batteries are running low. You can also turn alarms off through the app instead of having to push a button on the actual detector.

Which smoke alarm type is best?

While both types of smoke detectors are designed to help detect any house fire, no matter the source, each technology has its advantages and can offer an earlier warning over the other, depending on the origin of a fire.

The challenge is that it's impossible to predict which type of fire could erupt in your home, which is why the NFPA says the best protection is offered by having both alarm technologies in your home. There are a couple of ways to get this done.

If your existing detectors are ionization smoke alarms, you can purchase photoelectric smoke alarms and install one next to each ionization unit. If you don't know what type you have, check your owner's manual.

Another option: If budget allows, consider replacing all of your existing smoke alarms with dual-sensor devices, which combine both ionization and photoelectric technologies in a single unit.

As mentioned above, smart alarms can be hugely beneficial, as they alert you of warning signs at and away from home, and typically come as hybrid devices, says the New York Times, which consist of smoke, heat and CO detection technology.

Does the type of smoke alarm you have affect insurance rates?

The kind of smoke alarm you own might influence how much you pay for homeowners insurance. Insurance companies do look at the kind of smoke detectors you use at home.

If, for example, you have advanced smoke alarms that work really well, like those with special sensors or that connect to each other, insurance companies might think your home is better prepared for fires. As a result, they may lower your premium. Remember, each insurance company might think about smoke alarms differently, so it's good to talk to your specific insurer about how your alarms could affect what you pay.

Make sure smoke detectors are working properly

Knowing which type of smoke alarm you have is an important part of fire safety, but experts also warn that, regardless of type, smoke alarms won't protect you if they're not working properly.

According to the NFPA, an estimated 26 percent of smoke alarms failures were caused by dead batteries between 2014 to 2018. And in fires where smoke alarms were present but did not operate, 41% of the smoke alarms had missing or disconnected batteries.

So, start by making sure you have the right number of smoke alarms in the right places and each alarm has fresh batteries that are properly connected. The NFPA recommends a smoke detector in every bedroom, outside each separate sleeping area and on every level of your home (smoke rises, so install them high on the walls).

With a little preparation, your smoke alarms can be ready to alert you of a home fire, smoke or carbon monoxide.