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Optical smoke alarms, also known as photoelectric smoke alarms, work by ‘seeing’ the smoke and providing an audible alarm. Ideal for use at home in landings, hallways, bedrooms and living rooms, they have a quick response to visibly smouldering fires. This quick response and early alert gives you more time to escape from your home if a fire breaks out. Because of their advanced technology, optical smoke alarms are sometimes known as 'toast-proof alarms' as they are not prone to false alarms caused by fumes and steam from cooking. This makes them suitable for use in a hallway near a kitchen where false alarms from burnt toast may be common.Â
In the past, ionisation smoke alarms were recommended for homes. This technology has now been phased out in the UK, and optical smoke detectors are highly recommended as their replacement. This means that locations such as landings and hallways which previously had an ionisation alarm fitted, can now be fitted with an optical smoke alarm.
The Firehawk FHN250BB is a mains powered optical smoke alarm with an alkaline battery backup. It can be hardwired interlink up to 15 devices in one system including the Firehawk FHN250 or FHN450 alarms.
Optical smoke alarms, also known as photo-electric smoke alarms, are the most common type of sensor seen in households. This sensor type is suitable for rooms such as living rooms, bedrooms, and hallways. These are considerably safer than the previous sensor type, ionisation, as they do not contain any radioactive material. The advanced optical smoke sensor, means that they are less prone to false alarms caused by cooking fumes and steam, making them suitable for being installed near, but never in kitchens or bathrooms.
How do they work?
Optical smoke alarms work by 'seeing' smoke produced by slow smouldering fires, often a result of soft furnishings burning. The alarm works by using the light scatter principle, this is where a pulsating infrared LED operates within the alarm sensor, pulsing every 10 seconds to check for smoke particles. Once smoke particles are detected within the optical chamber, it activates the sounder alerting occupants to the fire. For further visual information on how optical smoke alarms work, please see our handy guide page.
Optical smoke alarms are best situated in rooms where soft furnishings are, such as bedrooms, living rooms, hallways, and landings. Within these rooms, it is recommended by the manufacturer that the alarm is installed on the ceiling, however there are exceptions where smoke alarms can be installed on the wall. The best installation locations are specified in the user manual supplied with any alarm.
Changing the battery in an optical smoke alarm all depends on how the alarm is powered. Some optical smoke alarms are powered by a sealed lithium battery and do not require to be changed for the entirety of their 10-year lifespan. After the 10-years, it is strongly recommended that the alarm is replaced in full, as the sensor deteriorates over time, making it less effective in detecting a fire and more likely to false alarm due to contamination.
Other optical smoke alarms are powered by a replaceable alkaline batteries, which through typical use, should be replaced every one to two years. For most of these types of replaceable batteries, the battery compartment can be found on the back of the alarm when removed from the base plate. When replacing a battery, it is key to remember that the replacement battery is one recommended by the manufacturer. Use of batteries which are not recommended, could result in the alarm not functioning as it should, or even fail to power the alarm at all.
The location of your alarm, or more specifically the temperature of the room, can affect the battery life in a smoke alarm. If the temperature is too cold, this affects the battery performance, and may reduce its efficiency.