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Smoke, Fire & Gas Detection FAQs

Why is my smoke alarm beeping?

If your smoke alarm is sounding continuously, first check there is no smoke or fire in your property. If no fire or smoke is present, or the alarm is beeping intermittently, there are three main reasons why this may be happening:

  • It could indicate the alarm is over 10 years old and needs replacing. View our range of smoke alarms to find a replacement.
  • There could be a build up of dust inside. To clean it, you can use a vacuum cleaner or hair dryer on a cold setting.
  • It could also be an issue with the power supply or the batteries may need replacing.

Read our in-depth smoke alarm troubleshooting guide to find a full list of reasons and solutions.

How often should I replace my smoke alarm?

You should replace your smoke alarm every 10 years. This is because the sensors in the alarm become less sensitive and may not activate when a fire is present.

Sign up to our smoke alarm reminder service to be reminded by text or email when your alarm is due to be replaced.

What is the difference between an ionisation and an optical smoke alarm?

Ionisation smoke alarms detect fast flaming fires, as such they may be prone to false alarming if installed near a kitchen. They are suitable for stairwells, landings and offices. Read more about how ionisation smoke alarms work.

Optical smoke alarms, also known as photoelectric detectors, have a high sensitivity to large particles in the air. They are slightly quicker at detecting slow smouldering fires that produce a lot of smoke (such as fire from soft furnishings). They are suitable for living rooms and sleeping areas and are used near kitchens as they are less prone to false alarms. Read more about how optical smoke alarms work.

See also heat alarms for the most suitable protection in a kitchen.

Why do your mains powered alarms have batteries?

All our mains powered alarms have a battery backup because, although mains powered alarms without this option do exist (BS5839 part 6 grade E), we regard them as far too dangerous. This is because a lot of fires are caused by electrical faults which would leave the building unprotected against fire if the smoke alarms had no backup battery. With our mains powered alarms you will always be protected.

Can I put my smoke alarm on the wall, or must it be mounted on the ceiling?

The best location to install your smoke alarm is in the centre of the ceiling rather than on the wall.

During a fire, smoke initially rises and then spreads horizontally. Placing the smoke alarm in the centre of your ceiling means that it is closest to all four points of your room. This ensures that you receive the earliest possible warning of a fire.

For more information, read our guide to positioning your smoke alarm and guide to which smoke alarms are best for each room.

How do I test my smoke alarm and how often should I test it?

We recommend testing alarms by pressing the test button built-in to the unit, as this is designed to simulate the detection of the target stimuli (usually smoke, heat, or CO) at the alarm sensor. For more detailed guidance, check the manual included with your alarm.

You should test your alarms regularly, preferably every week. Sign up to our free smoke alarm reminder service to receive regular reminders by email or text message.

What is the best way to dispose of an old smoke alarm or carbon monoxide detector?

Safelincs has signed up to Valpak's WEEE (Waste Electrical and Electronic Equipment) Distributor Take-Back Scheme*. This means if you are a Safelincs customer you can take old smoke, heat and CO alarms to your local recycling centre.

To find your nearest recycling centre, please visit Find out more about smoke alarm disposal.

*Registration ID: 7370

Is there a combination smoke alarm which will detect both a fire and carbon monoxide?

Yes, we sell a range of combined smoke and CO alarms which detect both fire and carbon monoxide.

We also sell combined heat and CO alarms which detect changes in temperature in a room rather than smoke. These are ideal for kitchens & garages where smoke or mist may often be present.

How do I fit my smoke alarm to the ceiling?

Smoke alarms can be either screwed to the ceiling using the holes on the base plate (screws provided) or fixed using a sticky pad.

Can air purifiers affect ionisation smoke alarms?

Yes, air purifiers may cause ionisation smoke alarms to sound falsely. To prevent this from happening, position the air purifier as far away from smoke alarms as possible.

Do you need an electrician to connect mains powered smoke alarms?

It is necessary that an electrician installs mains powered smoke alarms.

How long do smoke alarm batteries last?

  • 9V alkaline batteries last 12-18 months
  • Lithium batteries last around 5 years (some lithium cells are also rechargeable, and when used in a mains-powered alarm may last for the entire functional lifespan of the alarm)
  • Sealed lithium batteries last the lifetime of the alarm (usually 7-10 years)
Please note: the actual lifetime of your batteries depends on how often the alarms are tested or activated, as sounding the alarm draws more power than when the alarms are "waiting" to detect fire. You should also read your alarm's manual to make sure you only use the recommended types and brands of batteries, as failing to follow these instructions may cause the alarm to malfunction, not alerting you in the event of a fire, and might also invalidate the warranty.

I need to install a number of alarms to an existing panel mains system, but don't want to install new wires everywhere. Can I install wireless units that will link to the panel system?

You can install mains powered radio-interlinked alarms in the rooms and a mains powered alarm with an Ei128R base near the central control panel. The Ei128R base would then be connected with wire to the panel.

Are the battery radio-interlinked smoke alarms suitable to install in a four storey house with thick walls?

Our radio-interlinked smoke detectors have a radio frequency range of about 30 meters in buildings. This means that as long as the detectors are all within 30 meters of each other, the interconnection should be achieved. Some of the RF smoke alarms can also act as repeaters, which means that larger distances can be achieved. So, a four storey house should normally be suitable for RF install.

Is there a radio-interlinking alarm system that will cover a large three storey house? If one is activated they all need to go off.

Our radio-interlinked alarms are designed to have 12 smoke alarm units interlinked with each other in any one series. However the alarms are able to recognise more than 11 other smoke alarms but there will just be no visual confirmation on each unit when going through the initial house coding procedure. Interlinking 12 alarms with 6 call points should work together providing each unit is no more than a 30m distance apart. Larger distances can be covered by using one of the smoke alarms in repeater mode, activated by flicking a switch.

If a false alarm goes off can pressing the hush button on any of the interlinking alarms stop all the units beeping?

No, to stop the alarms from sounding the hush button on the unit that started the process needs to be pushed. Pressing any other unit will just silence that one unit. The unit can be identified by the rapidly flashing red LED.

How do radio interlinked smoke alarms work?

Several RF smoke alarms form a group which has the ability to recognise each other's signals. If one of these alarms detects fire, it sends a digitally coded signal to the other alarms which then also sound an alarm. Radio-interlinked smoke alarms are used in larger houses, small commercial premises and wherever there is a risk that not everybody in the building will hear a fire alarm from a different part of the building.

How can the alarms interconnect without a cable connection?

Radio-interlinked smoke alarms replace the signal cable between alarms with RF communication. A radio signal is sent when the test button is pressed, or the alarm senses smoke. This is received by all the interlinked alarms in the system and will cause all alarms to sound.

How can I protect my family from CO poisoning?

Make sure rooms and heaters are well ventilated, have your chimneys and flues checked regularly, make sure boilers and heaters are maintained and serviced regularly. Buy a carbon monoxide alarm/detector. A carbon monoxide alarm will measure the concentration of carbon monoxide in a room and sound an alarm if the CO concentration is higher than permitted

What is carbon monoxide?

Carbon monoxide (chemical symbol: CO) is a colourless, odourless, tasteless and toxic gas created by the incomplete combustion of fossil fuels (gas, oil, coal and wood) used in our everyday appliances such as heaters, engines and boilers.

Protect yourself and your family by purchasing a CO detector and learning about the symptoms of carbon monoxide poisoning.

Why is my mains powered smoke alarm beeping just after it has been installed?

There are a number of possibilities why mains powered smoke alarms might beep after an install:

  1. The cable connection is incorrect, resulting in the alarm not receiving mains power. This leads to a warning and eventually low battery.
  2. If the alarm is connected to a nearby lighting circuit the connection might be wired incorrectly, interrupting the power supply when the lighting is switched off.
  3. The fuse to which the alarm is connected has not been switched back on. This is a very common occurrence.
  4. Sometimes, the back-up battery of a rechargeable smoke alarm takes time to reach operating level and the alarm might beep for a short time.

Read our smoke alarm troubleshooting guide to find a full list of reasons and solutions.

Which smoke alarm should I use in a bedroom with an en suite bathroom?

We recommend installing an optical smoke alarm in a bedroom with an en suite bathroom.

It would be less likely to sound a false alarm if steam or water droplets were to come into contact with the smoke alarm. They are also slightly quicker at detecting slow smouldering fires that can originate from upholstery and over-heated wiring. 

Detectors should usually be installed as central to the room as possible. However, we recommend ensuring your detector is not installed directly in the path of the bathroom door as smoke alarms are not designed for use in bathroom areas.

How many alarms can be wirelessly interconnected using radio frequency?

This depends purely on the model and manufacturer of the alarm or system you are planning to install. Some models will allow 12 to 15 alarms to connect wirelessly, whereas other newer models can interlink with up to 50 other devices.

Please view our range of Radio-Interlinked Alarm Systems.

How can I make sure I hear the smoke alarm?

To ensure you hear the smoke alarm when it detects a fire you should have radio-interlinked alarms. If one of the alarms detect a fire then all the other alarms in the system will sound which will greatly increase the chance of the occupant hearing the alarm.

If the occupant has a hearing impairment there are fire detection systems for the deaf and hard of hearing that feature strobe lights and vibration pads to ensure the occupant will be alerted in the event of a fire.

How can I test my heat alarm?

All of our heat alarms have test buttons. Press the test button for about 5 seconds regularly to ensure your alarms are operating correctly.

If you wish to test the heat sensor of the alarm, our advice is to use a solo 400 series tester or call a fire alarm servicing company.

Where should I install carbon monoxide detectors?

CO detectors should be installed near boilers and other potential sources of carbon monoxide.

Place the detector 1 to 3 meters away from the boiler, etc. to avoid small start-up CO discharges to cause false alarms.

It is advisable to install detectors in areas of your home that you spend the most time in such as the living room and bedrooms. Larger homes may require several detectors to cover the property fully.

Please note: we recommend referring to the manufacturer installation guide that came with your detector for full instructions.

What are the symptoms of carbon monoxide poisoning?

The symptoms of CO poisoning can range from mild flu-like symptoms such as headache, drowsiness, confusion, nausea and dizziness to more severe symptoms like breathing difficulties and irregular heartbeat. CO poisoning can ultimately lead to coma and death.

View more symptoms on our carbon monoxide information page.

How do I radio-interlink compatible smoke and heat alarms that are 'interconnectable'?

Generally, the process for interlinking hardwired alarms is the same. Firstly, you need to make sure that the alarms you are purchasing are compatible with each other, as alarms from different manufacturers (in most cases) do not mix. Dependent on the manufacturer's instructions, you will then be advised to use either a length of bell wire / twin cable to serve as an interlink cable, or 3-core and earth (which is usually adopted in newer installations).

In the same way as interlinking hardwired alarms, it is still crucial to check compatibility between alarms for systems that link wirelessly. The way in which radio-interlinked alarms are connected can differ from brand to brand, however there will be instructions included with the alarm to guide you through the interlinking process. No signal cables are required between radio-interlinked alarms.

Related videos:

Can smoke alarms detect carbon monoxide gas?

Only combined smoke and CO alarms can detect both fire and carbon monoxide gas.

Can the sound level of smoke alarms be increased if they are used for hard of hearing?

Unfortunately the sound level on a smoke alarm cannot be adjusted. However, we offer a range of smoke alarm systems for people with hearing impairments which instead use strobe lights and vibrating pads to alert you of a fire.

Are there any restrictions to the distance a radio-interlinked smoke alarm will work?

Most radio-interlinked alarms have a range of 150 meters in an open space and up to 30 meters in buildings. The thickness of the walls and partitions will affect the travel distance of the signal.

Do all my mains powered RF alarms need connecting to the power supply?

Yes, all your mains powered radio frequency smoke alarms will need connecting to the power supply.

If you are retrofitting your RF alarms the electricity supply can be taken from the nearest light fitting. In new builds the electrician will create a dedicated electrical circuit for the alarms.

If your mains powered smoke alarms are not radio-interlinked you will also need to connect your alarms with a signal wire.

Which smoke alarms can be interlinked?

All mains powered smoke alarms can be interlinked, as well as some battery alarms.

Mains powered smoke alarms can be interlinked via a radio signal (for RF alarms) or via a signal wire for alarms that do not have RF, such as Kidde, Aico Ei & FireAngel

Battery radio frequency smoke alarms, such as UltraFire, Ei and Firehawk can also be interlinked. 

Do batteries in radio-interlinked alarms expire quicker than those in normal alarms?

Batteries in radio-interlinked alarms do expire quicker than in other smoke alarms. This is due to the frequent radio interaction of the alarms to ensure that when one smoke alarm is activated, they all go off.

RF smoke alarms are, however, also available with a 10 year sealed long life lithium battery. This battery will last for the 10 year life of the smoke alarm.

Which smoke alarms should I use in a bed and breakfast?

We recommend long life battery powered smoke alarms for B&Bs as they contain 10 year lithium batteries which last the full life of the detector. We also offer a radio-interlinked option so if one alarm detects a fire, all connected alarms go off.

Alternatively you can install mains powered alarms which are also available with longlife backup batteries and wireless interlinking.

What type of smoke alarm do I need?

We recommend using an optical smoke alarm in hallways, living rooms, dining rooms and bedrooms, as they are good at detecting smouldering fires from soft furnishings and are less likely to be set off by cooking fumes from a connected kitchen.

Ionisation alarms are recommended for landings as they are designed to react quickly to fast flaming fires.

Heat alarms are recommended for kitchens and garages as they do not sound false alarms from cooking fumes, vehicle fumes or steam.

Which smoke alarm has a relay contact to connect to a GSM dialer?

For a hardwired connection throughout the property, the Ei128R 5A relay base and Ei128RBU 5A relay with backup battery from Aico / Ei Electronics work in conjunction with the Ei140 series (alkaline backup) and Ei3000 series (lithium backup) mains-powered smoke, heat, and combination alarms. The alarms must be interlinked to the relay via a wired connection but can be installed directly on top of the relay to "hide" it, or separately from the relay if the location of the alarm is not a convenient place to connect with the GSM dialer.

If a wired connection between the relay and alarm is not feasible or desirable, but mains power is available, any RadioLINK-capable alarm from Aico or Ei Electronics such as the Ei600RF battery-powered series, Ei140RF mains-powered series with alkaline backup using the Ei168RC radio base, or Ei3000RF mains-powered series with lithium backup using the Ei3000MRF radio module can be wirelessly connected with the Ei428 radio-interlink relay with backup battery instead. The Ei428 still needs its own mains power feed, but does not need a direct hardwire connection to any alarm, making installation much more flexible.

Please Note: If you want the GSM dialer to operate during mains power failures it would need its own backup power source, and you must use either the Ei128RBU or Ei428 relays which also have their own backup batteries.

Is there a carbon monoxide alarm for the hearing impaired?

Yes, we supply the Ei170RF, a strobe and vibration pad for the deaf and hard of hearing which can be linked to the following CO detectors:

Can mains powered smoke alarms be connected to the mains power via the lighting circuit?

Yes, hard-wired mains powered alarms can be wired to the unswitched live feed of the nearest frequently used lighting circuit.

Is there a way to control an interlinking smoke alarm system?

Yes, many manufacturers offer additional accessories which connect to existing systems to help manage them.

Some Aico / Ei models, for example, have the option to incorporate a manual call point, as well as test, silence and control switches so the alarm can be tested at ground level rather than reaching up to the ceiling.

Many manufacturers, including Aico / Ei and FireAngel, are also introducing Smart Home technology which, when using the appropriate module / gateway, will allow users to view the alarm system from their smartphone, as well as receive notifications of alarm activations, and test, silence and locate alarms via a smartphone app.

Which smoke, heat & CO alarms are suitable for the 2022 Scottish regulations?

From February 2022 all homes in Scotland must be fitted with interlinking smoke and heat alarms. In addition carbon monoxide alarms are required if there is a carbon-fuelled appliance or flue. View our list of alarms suitable for the Scottish regulations.

Where should I position my carbon monoxide alarm?

In order to work effectively, CO detectors:

  • Should not be placed above or below windows
  • Should not be placed above radiators
  • Should be placed 1 to 3 metres away from solid fuel appliances

Please see our video on where to install a CO detector for information on how to fit your CO alarm to the wall.

How do I pair the Firehawk W Series radio-interlinked smoke & heat alarms?

Please see our instructional video on how to interlink the Firehawk W Series alarms.

What is a masking plate?

A masking plate is used when replacing older, rectangular smoke alarms with new circular models. The plates cover any marks left by the previous unit and maintain the aesthetics of a room.

Why is my smoke alarm flashing red?

The reason why the LED light on your smoke alarm is flashing or blinking red (or green) will vary depending on the model and manufacturer. The best option is to check the instruction manual for your specific smoke alarm model. Smoke alarm instruction manuals are available to download on the ‘Technical Data’ tab on most of our smoke alarm product pages.

In some models of smoke detector a red or green LED light flashes periodically without an alarm sounding to show that it is receiving power and is operating normally. Other reasons for smoke alarms flashing red or green could include an end of life or low battery warning, to indicate that the alarm is in hush mode or that there is a fault with the alarm.

Can a wireless router interfere with radio interlinked alarms?

A wireless router is very unlikely to interfere with the signal of your radio interlinked smoke, heat or CO alarm as the RF signal is digitally coded.

Which radio-interlinked smoke alarms do I need in my home?

Some optical smoke alarms and heat alarms can be combined into one radio-interlinked system. Optical alarms are most suited to hallways, landings, living rooms and bedrooms whereas heat alarms are best for the kitchen and garage. You can purchase the radio-interlinked alarms separately or as a complete home alarm kit. Our Smoke Alarm Buying Guide explains more about smoke alarm types.

Why is carbon monoxide dangerous?

Carbon monoxide (CO) is a colourless, odourless, tasteless gas which makes it difficult to detect. Inhaling CO reduces the blood's ability to carry oxygen to the body's organs and cells.

Each year, over 50 people die in the UK as a direct result of exposure to carbon monoxide. Many more people die through strokes and respiratory illness made worse by inhaling low levels of CO over prolonged periods.

To protect yourself and your family, purchase a carbon monoxide detector and use the test button weekly to check it is in working order.

When the test button is pressed on an interlinking smoke alarm will this cause all the other units to go off, too?

Yes, pressing the test button on one interlinking smoke alarm will activate all the linked units. To find out how to link your smoke and heat alarms, please refer to the manufacturer's instructions which can be downloaded from the relevant product page on our site.

Should I buy smoke alarms or heat alarms for my thatched property?

We recommend using ionisation smoke alarms in the loft of the property as they are the quickest to detect fast flaming fires such as a fire originating from a thatched roof, giving you the best chance of stopping it in its tracks.

For bedrooms, living rooms, downstairs hallways and rooms adjacent to the kitchen we recommend using optical smoke alarms as they are quicker to detect slow smouldering fires that originate from upholstery type materials or overheated wiring. This newer sensor technology is less prone to false alarms caused by fumes such as those created by everyday cooking and fire places under normal, safe circumstances.

For kitchens and garages, we recommend using heat alarms as they detect heat and not smoke, making them ideal for rooms where smoke fumes, vapours, dust, and damp are common.

Where should I install my carbon monoxide detectors?

Wall mounted carbon monoxide detectors should be placed 1m to 3m horizontally from the appliance at around the same height – i.e. not above a stove where it would be in the path of steam or fumes.

Combined smoke & CO alarms or mains-powered CO alarms are typically installed on the ceiling and should be at least 30cm away from any wall.

Do not install CO alarms above or below windows, or in dusty areas such as workshops or garages where the alarm can become contaminated.

For more information please check the manufacturer's instructions. You can download the PDF manual from the relevant product page on our site. You can also watch our video guide to positioning CO detectors.

How do I operate magnetic door retainers using a smoke alarm system without central panel?

The easiest option would be to use hardwired alarms from Aico / Ei Electronics in conjunction with their relay bases. The Ei140 series (alkaline backup) and Ei3000 series (lithium backup) mains-powered smoke, heat, and combination alarms interlink with each other and are compatible with the Ei128R 5A relay base and Ei128RBU 5A relay with backup battery. The relays must be connected to the alarms via a wired interlink but are flexible in terms of location: they can be installed separately from the alarm in a convenient place to connect with the retainer system, or between the alarm's mounting base and ceiling to "hide" the relay.

If a wired connection to the alarm is not feasible or desirable, but mains power is available, the Ei428 radio-interlink relay with backup battery instead connects wirelessly with any RadioLINK-capable alarm from Aico or Ei Electronics. This would allow for both mains-powered (alkaline / lithium) and battery-powered alarms to be used to operate the magnetic door retainer system.

These relay bases are triggered when the connected alarm activates, and would be installed and connected to the magnetic door retainer system (by a competent electrician) in such a way that the retainer is deactivated or power to the retainer is cut. This would allow the automatic door closer to do its job: closing the fire door and slowing the spread of smoke and fire through the building, helping occupants to escape safely.

Please Note: If the magnetic door holder has a backup power source so that it continues to operate during mains power failures, relays with their own backup batteries, such as the Ei128RBU or Ei428 relay, are required.

What are the regulations for testing CO detectors? Do I need to use test gas?

A weekly check with the test button is sufficient if you choose a high quality CO detector. There is no legal or BSI requirement to test the CO detectors with a test gas.

How do I replace my smoke alarm battery?

Please see our smoke and CO detector videos for instructions on how to replace the battery for different alarm models.

What level of carbon monoxide is dangerous?

Prolonged exposure to carbon monoxide levels of 10ppm (parts per million) or above is shown to have adverse effects on the body and brain.

Concentration of CO in the air Implications of Exposure
10 parts per million (ppm) Threshold at which prolonged exposure can have adverse effects on the body and brain.
50 parts per million (ppm) Safety level as specified by the Health and Safety Executive for a maximum of 30 minutes.
200 PPM Slight headache within 2-3 hours.
400 PPM Frontal headache within 1-2 hours, becoming widespread in 3 hours.
800 PPM Dizziness, nausea, convulsions within 45 minutes, insensible in 2 hours.

See our carbon monoxide information page for more details.


(doc:536 V1.0). Our articles are reviewed regularly. However, any changes made to standards or legislation following the review date will not have been considered. Please note that we provide abridged, easy-to-understand guidance. To make detailed decisions about your fire safety provisions, you might require further advice or need to consult the full standards and legislation.