The most important things to know

to choose meaningfully.


Smoke and carbon monoxide (CO) detectors are devices conceived to detect and alert (via acoustic and other alarm types) about the presence of a fire inside a building. These devices can detect the presence of smoke (air-suspended particles generated from inefficient combustion) and carbon monoxide (a colourless, odourless and killer gas that results from the incomplete combustion of fuels such as oil, wood, coal, natural gas, propane, methane and gasoline that at home is mainly generated by heating and cooking systems).

Smart smoke & carbon monoxide detectors additionally will inform about the presence of a fire regardless of where you are and with a wider variety of alarm types. Some of them can interconnect (so to make the alarm present to other areas of the home) and even indicate you the way out through integrated lights.

These devices can be an excellent solution to prevent fire and CO associated dangers. In the period 2012-2016, 7 people per day died on average in the US due to home fires1. Carbon monoxide has a notable impact on our health and lives as well, especially on infants and the elderly. The symptoms of CO poisoning (by short but intense or low but long exposures to the gas) are vomiting, headache, dizziness, confusion, causing even the death. In the period 2010-2015, a total of 2.244 persons died from unintentional CO poisoning2. In addition to the number of deaths, fires and elevated carbon monoxide concentrations have a relevant impact on injuries and property damages.


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Time saved thanks to the possibility of running tests automatically.

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Quality of life improved thanks to increased visibility on home environment conditions.

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Peace of mind increased thanks to increased visibility of what happens at home and a decreased reaction time in case of fire or dangerous CO concentration levels.

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No direct impact on home costs.


Smoke and CO detectors can be classified attending several aspects. It can be, for instance, distinguished between the internet and non-internet connected devices, or between the battery and hard-wire powered devices. However, the technology used on smoke and CO detectors provides a clear way of classifying them:

These are suitable for the detection of flaming fires. It is advised to avoid its' installation in areas where steam and other smokes are usually generated (bathroom, kitchen). These alarms are made of two separate metal plates that are electrically charged, and a radioactive substance that converts the air molecules flowing between the two plates into charged molecules, closing in this way the electric circuit. When smoke enters into the smoke detector, it breaks the flow of icons between the two electric plates, opening the electric circuit and activating the alarm.

These are suitable for the detection of long-period smouldering fires. These alarms are made of a LED that emits a light beam in a straight line and a light sensor. In normal conditions, the light beam does not impact the sensor. Instead, when smokes enter into the smoke detector, the light beam is interrupted, making that some of the reflections impact the light sensor and as a consequence, the alarm goes off.

These detectors work based on a chemical reaction that occurs when CO enters into the detector. The chemical reaction generates an electric current and is by measuring it that the concentration of the CO is determined. Based on the readings, the alarm then goes off.

These detectors work based on a gel that changes colour when in contact with CO. The colour change is then identified by a separate sensor that processes the information to the central processor, which in turn makes the alarm goes off.

These detectors rely on the change of resistivity of a metal oxide surface. When CO enters in contacts with the metal oxide surface, it reduces the resistivity. This change is then read by the central processor, which activates the alarm.

There are some solutions in the market that combine more than one technology in a single detector.


Before buying a (set of) smoke and carbon monoxide detector(s), there are some variables that we retain worth considering:

For best protection, it is advised to use a combination of the different technologies available for smoke and CO detectors. So you may want to look for a detector that ideally includes all the other kind of sensors. At the same time, we encourage you to consult your local code. These can consist of regulations that require you to install a specific number and type of sensors based on the number of rooms and the home size.

There are smoke and carbon monoxide detectors that are directly wired to the electrical grid of your home. These usually include a backup battery to keep the system functioning in case of a power outage. There are also battery-powered devices that make the installation easier. Depending on the battery included, you might be able to use the same one without having to replace it during the whole life of the smoke and/or CO detector. So you may want to take a look at the battery life.

Generally, wired smoke and CO detectors are interconnected so that if one of the installed detectors goes off the rest will follow. As well, some wireless smoke & carbon monoxide detectors can communicate with each other. This is a critical feature, especially for large and multi-level houses where occupants are not close to each other. In any case, for proper interaction between devices, it is advised to install models of the same brand.

Some detectors combine different types of alerts so to adequately warn you of a potential safety issue both when you are at home and when you are away. The most common type of alerts are audible alerts (emit a sound), visual alerts (emit light) and remote mobile alerts (send a push notification, email and others).

Some devices are able to run the recommended tests autonomously. These tests make sure that the alarm works appropriately, saving time to the user and increasing the peace of mind.



Place the detectors according to what it is indicated by the local code and the manufacturer of the devices. As a general rule, smoke and CO detectors should be installed in the ceiling (or high on a wall) of each area between sleeping rooms and on every level of the home (including the basement). Smoke detectors should additionally be installed in bedrooms.


Interconnect the different detectors. In the case of using smart detectors, you may want to apply specific automation rules. For instance, depending on the location of the detector that goes off, you may want to turn on a particular light that illuminates the way out of the house.


Test the detectors according to manufacturer indications, generally every month. Avoid burning any kind of product indoors to prevent the emission of CO.


Replace the detectors according to the manufacturer's indications. Generally, smoke alarms need to be replaced after ten years and carbon monoxide detectors after five years. It is an excellent practice to substitute all the devices at the same time and to stick to a unique manufacturer. Check that device run properly and do regular checks of ducts and chimneys.


National Fire Protection Association. Home structure fires. NFPA Research. 2018. <https://www.nfpa.org/-/media/Files/News-and-Research/Fire-statistics-and-reports/Building-and-life-safety/oshomes.pdf>.
2 Centers for Disease Control and Prevention, QuickStats: Number of Deaths Resulting from Unintentional Carbon Monoxide Poisoning,* by Month and Year — National Vital Statistics System, United States, 2010–2015. Accessed August 2019. <https://www.cdc.gov/mmwr/volumes/66/wr/mm6608a9.htm>.

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