Smoke Sensor

A smoke sensor is a device fitted to smoke alarms. A smoke alarm is designed to detect the presence of smoke in a home to alert the occupants that a fire has broken out. A smoke alarm contains not only a smoke sensor but also a loud audible alarm (85 decibels on average) to alert people in the home. Detecting the smoke from a fire and sounding the alarm enables the occupants to get out and alert the fire service quickly. In fact, installing a smoke sensor is vitally important and can save lives.

How does a smoke alarm work?

In a smoke alarm, the smoke sensor is designed to detect suspicious smoke. Although ionisation chamber smoke alarms are available, they're not permitted for use in private residences because they contain a radioactive component. The only smoke alarms currently authorised for domestic use are optical alarms (also called photoelectric smoke alarms).

• How does optical detection work?

An optical smoke alarm contains a photoelectric sensor, which measures variations in a light signal emitted by an electroluminescent diode. Under normal conditions and if no smoke is present, the signal is continuous and normal. However, if the light signal is disrupted by the presence of smoke, the optical sensor perceives a disruption and an audible alarm is triggered.

Although the optical detection process may vary depending on the product used, it always involves capturing variations in a light signal emitted by a diode. A linear optical smoke alarm detects any change in light intensity between the diode and the photoelectric sensor. Other smoke alarms reverse the process: the light signal is pointed next to a photoelectric cell and if this signal is dispersed by the smoke, the optical sensor perceives the light and the alarm is triggered.

• Powering a smoke alarm

A smoke alarm can be powered by connecting it to the power circuit in the home. However, most smoke detection devices are powered wirelessly using batteries. Some smoke alarms require alkaline batteries, while other products are fitted with a lithium battery. An alkaline battery needs to be changed every year on average and an audible alert indicates that the battery is running low. Lithium batteries have the advantage of lasting 10 years and therefore require less attention. However, this type of battery can't be changed, meaning that the smoke alarm can no longer be used when the battery dies. When it stops working, the smoke alarm will need to be replaced.

The choice of battery is important, as it affects the price of the smoke alarm. A product that has a lithium battery is more expensive than a device powered by alkaline batteries, although it is safer (there's no danger of it not working when the battery runs out) and can be less expensive in the long run taking into account the price of replacement batteries over the lifespan of a product with alkaline batteries.

It's also worth noting that all smoke alarms are designed to operate continuously: they alert you when the battery is running out, while products connected via a cable contain a backup battery in case there is a power cut. Discover all our products

Why install a smoke alarm in your home?

A smoke alarm is an essential product for protecting your home from fire.

• Smoke alarms are mandatory

Since 2015, it has been mandatory for every home in France to be fitted with at least one autonomous device that detects smoke and triggers an alarm. This legislation, approved in March 2010, applies to all residences: houses, apartments, furnished accommodation, seasonal rental properties, etc. A smoke alarm is designed to detect the start of a fire in a home as soon as possible in order to quickly alert the occupants. This legislation requires smoke alarms to bear the CE marking and comply with the European standard EN 14 604.

All owners of a residence are therefore required to fit a smoke alarm. If an apartment is rented, the tenant and owner must both make sure that the smoke alarm is compliant and working properly when the check-in inventory takes place. It's then up to the tenant to maintain the device, regularly check that it works and change the batteries.

• The risk of domestic fires

The risk of a domestic fire is higher than you might think. Every year in France, the fire service responds to no fewer than 280,000 calls and nearly 800 deaths are caused by fires. Since the installation of a smoke alarm in every home was made mandatory by law, the number of domestic fires has fallen by 4% and the number of victims has declined. In countries where this type of legislation has been in place longer, there has been as much as a 50% fall in the number of fire-related deaths.

When a fire starts, it's often necessary to react very quickly. A fire spreads rapidly and the toxic smoke gradually saturates the air, causing asphyxia. That's why early detection of smoke is essential for giving the home's occupants enough time to get out and alert the emergency services.

• A smoke alarm can alert you during the day or night

The volume of an alarm is also a crucial factor in how effective it is. Most fatal fires occur at night, when the occupants of a home are asleep. That's why the audible alarm must be at least 85 decibels in order to be heard by someone who's asleep and alert them quickly enough.

It's a common misconception that the smoke, smell, heat or noise from a fire is enough to wake up a person. A fire produces highly toxic smoke that poses a danger well before the effects of the fire (heat, noise) wake up someone who's asleep. A smoke alarm significantly increases your chance of being alerted in time and exiting the building.

Installing a smoke alarm

You don't need any special skills to install a smoke alarm and the process is very quick. Nevertheless, it's important to carefully choose where you position a fire detection device to make sure it's working properly, both in terms of detecting smoke and ensuring the alarm can be heard properly throughout your home.

• Installing a smoke alarm

To install a smoke alarm in the right place in your home, choose a central area such as a corridor that leads to the main rooms. The alarm should be placed sufficiently near the main room so that it can be heard at night in case of a fire. Avoid placing it nearby the kitchen, bathroom or laundry room, as smoke or steam could set off the alarm.

The position of a smoke alarm is also crucial for making sure your home is safe. Ideally, place it on the ceiling (smoke tends to rise due to its heat) at least 60 cm from the walls. If you can't install your smoke sensor on the ceiling, place it on a wall at a height, near the ceiling.

This stage of the installation is crucial. Take your time to determine the right position for your smoke alarm. The safety of the people in your home in case of a fire depends on it. If it's incorrectly positioned, your smoke alarm might detect smoke too late and not give you enough time to exit your home or the alert the fire service.

If your home has a large surface area or several floors, remember to install several smoke sensors at different strategic locations in your home and at least one on each floor. You can also install a smoke alarm in your garage or cellar so that you'll be alerted if a fire breaks out in these areas.

• Choosing the right smoke alarm

Firstly, you need to make sure you're complying with the law and choose a smoke alarm that meets the European standard EN 14604 and bears the CE marking. Next, bear in mind the options available on existing products: an insect screen can be useful to prevent false alarms, while a test button allows you to regularly check that your smoke alarm is working. Some smoke alarms also have a feature to detect carbon monoxide, an odourless and highly dangerous gas that can be given off by a defective heating system. Although this option is beneficial for your safety, it's difficult to find a position in your home that perfectly suits both sensors for optimal functioning.

Some of the most sophisticated products in terms of safety include smart smoke alarms. A smart smoke alarm works in a similar way to a standard device: if a sensor detects the presence of smoke in the home, an audible alarm is triggered to alert the occupants. However, a smart smoke alarm also alerts you directly on your smartphone (and also warns other members of your family who you've linked to the smoke alarm using the management app). This alerts you even if you're away from home, enabling you to call the emergency services from where you're working or staying while on holiday.

The Netatmo Smart Smoke Alarm also offers other very useful features, such as the automatic operation test, which regularly checks that the smoke alarm is working properly, and the battery alert, which notifies you when the smart smoke alarm needs to be replaced.