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Can a humidifier set off a smoke alarm?

Smoke detectors are installed to warn us of any mishap caused by fire, these useful devices save countless lives and property on a daily basis. We can find smoke detectors everywhere – homes, offices, movie theaters, shopping malls, and so on. This brings us to a question: Can a household appliance such as a humidifier trigger a smoke detector?

A humidifier can trigger a smoke detector as it cannot differentiate between smoke and water particles. There’ve been incidents where high levels of humidity in places have triggered smoke detectors. Since humidifiers increase air humidity levels, they cause smoke detectors to trigger.

This article will further discuss the types of smoke detectors and humidifiers, how they work, how humidifiers trigger smoke detectors, and ways to avoid this false triggering. 

Can a humidifier trigger a smoke detector
Can a humidifier trigger a smoke detector

Humidifiers: An Overview

 Humidifiers are home appliances that increase the moisture levels in the air. They are used in a single room or entire house through the HVAC system. Humidifiers are important as they counter the drying of the mucous membrane in extremely dry conditions. Even medical ventilators have humidifiers to comfort an ailing patient.

Humidity can be measured by a hygrometer. It is measured as RH (Relative Humidity). For domestic purposes, relative humidity of 30% to 50% is recommended in most cases. Abnormal humidity levels cause several problems.

Low humidity levels can lead to irritation in your throat and nasal passage, cause your skin to dry or result in itchy eyes.

High levels of humidity can make you feel stuffy and promote microorganism growth in your house. This, in turn, can lead to allergies and other diseases.

There are several types of humidifiers. The major ones are:

  • Ultrasonic humidifiers: These humidifiers vibrate a ceramic diaphragm at high frequency to create tiny water particles that exit the humidifier as a white mist.
  • Impeller humidifiers: They have a rotating disc that throws water at a diffuser to break it into fine droplets that float into the air.  
  • Evaporators: These devices have a porous wick that absorbs water and provides a large surface area for it to evaporate. The fan blows air through the wick to aid water evaporation.
  • Steam vaporizers: It heats water through electricity to generate steam, which leaves the vaporizer after it is cooled. 

So you can see that humidifiers form tiny water particles that float in the air and increase the overall moisture content of a place. This is an important observation, as we will see shortly. Just for the sake of completeness, to reduce humidity, you can use a dehumidifier or an air conditioner to absorb the excess water content in the air.  

Smoke Detectors: A Quick Outline

 A smoke detector is a device to sense smoke as a sign of fire and cause an alarm. These electronic devices have saved lives and property throughout the world. The US National Fire Protection Association reported that for the period of 2009-2013, there had been 0.53 deaths per 100 fires at homes having working smoke detectors in comparison to 1.18 deaths in homes without working smoke detectors. 

Interestingly, the first smoke detector was patented by Francis Robbins Upton, an associate of Thomas Edison. The modern smoke detector is credited to a Swiss physicist, Walter Jaeger. In an attempt to create a poison gas sensor in the 1930s, he created the first ionization smoke detectors. The first ionization smoke detectors were sold in the US in 1951.

There are mainly two types of smoke detectors: Ionization smoke detectors and photoelectric smoke detectors. Find below a brief description of their work.

Ionization smoke detectors

These smoke detectors use a radioisotope like Americium-241 to ionize the air. It has two chambers with pairs of electrodes within them. One chamber is open to the air, and the reference chamber is sealed from the outside world. 

The radioisotope source ionizes the air in both the chambers. The electrode pairs in each chamber have a potential difference across itself, polarizing the ions in the air gap between each chamber’s electrode pairs and allowing a current to flow in-between them.

In normal circumstances, the currents would be the same in both the chambers. When smoke particles enter the open chamber, it attaches itself to the ionized air molecules, reducing the number of ions for current conduction. This reduces the current in the open chamber as compared to the closed chamber, triggering the smoke detector to raise the alarm.

Photoelectric smoke detectors 

These detectors have a light source, such as a Light Emitting Diode (LED) or an incandescent bulb emitting either infrared, visible, or ultraviolet light; a lens and a photoelectric receiver such as a photodiode

When smoke reduces the light intensity (due to scattering) from the light source to the photodiode, the associated circuitry triggers an alarm. Alternatively, in some cases, when light is scattered by the smoke particles, it then falls on the photodiode causing the smoke detector to raise the alarm. In either case, you can see that the smoke molecules scatter the light causing the smoke detector to start an alarm.

Can a Humidifier Trigger a Smoke Detector?

 You can infer from the previous section that a smoke detector is triggered in two ways:

  • Due to change in electrical conduction by smoke particles between electrodes in Ionization smoke detectors. 
  • Due to the scattering of light by smoke particles in Photoelectric smoke detectors.

In other words, the smoke detectors do not actually detect smoke but simply infer their presence due to the change in electrical conductivity or light intensity. Thus, any particle of the size of smoke particles, such as fine water droplets from humidifiers, can cause the triggering of a smoke detector. 

While comparing both the smoke detectors, it has been found that Ionization smoke detectors are more sensitive to humidity than photoelectric smoke detectors. In fact, Photoelectric smoke detectors have been found to be useful in detecting fire that begins with a long-smoldering.

How to Reduce False Triggering of Smoke Detectors by Humidifiers?

Though smoke detectors are useful gadgets, their false triggering can be an irritant at times. Hence it is better to take measures to avoid this problem. You can refer to the following points for the same:

  • Place the smoke detectors in the right location. Keep them away from places where you will be using humidifiers or from places like the kitchen, washroom, etc.
  • Try to control the humidity within the normal range. Do not continuously use a humidifier, or use exhaust fans or any other way to increase ventilation.
  • If your smoke detector has sensitivity adjustment, do so to avoid false triggering.
  • Clean the outside of a smoke detector regularly to remove any condensed water on its outer casing. Also, remember to have it serviced regularly. 
  • Use both types of smoke detectors (Ionization and Photoelectric types) in parallel for better immunity from false triggering.


We understood the working of humidifiers and smoke detectors to gain a clear insight that humidifiers can actually trigger a smoke detector. Smoke detectors do not detect smoke but infer their presence from the change in electrical conductivity or light intensity. 

In other words, since smoke detectors cannot distinguish between smoke particles and fine water droplets, they get triggered by either of them. 

We also came to know of various precautionary measures to avoid false triggering. Since smoke detectors are life saviors, it is essential that we incorporate them wherever required. By following these simple steps, we can ensure that smoke detectors don’t get triggered by humidifiers.  


  • Vincent Steele

    Vincent is a freelance writer based in Santa Ana, California. When he isn't writing articles for Temperature Master, he can be found biking or hanging out with his cat, Shelly.