How many do you need?

The simple answer is, "The more alarms you have, the safer you'll be".   As a bare minimum you should have one on each floor. However, if you have only one alarm and two floors, put it somewhere you’ll be able to hear it when you're asleep.

If you have a TV or any other large electrical appliance (such as a computer/washing machine/drier) in any of the upstairs rooms, you should fit a smoke alarm there too. In addition unplug the appliance when it's not in use!

Choosing a smoke alarm or heat alarm

In simple terms there are two types of smoke alarm and a heat alarm:

Ionisation alarms

Ionisation type sensors are particularly sensitive to the almost invisible smoke produced by fast flaming fires. This makes them more liable to false alarm due to cooking fumes if sited in a hallway close to a kitchen. Ionisation alarms are less vulnerable to false alarms caused by dense tobacco smoke, excessive dust and insect ingress. The BS 5839: Pt.6: 2004 Standard recommends that ionisation alarms should not be used in hallways and landings,where there is a risk of false alarms caused by cooking fumes.

These are the cheapest and most readily available and are very sensitive to flaming fires (ones that burn fiercely such as chip-pan fires). Ionisation alarms will detect flaming fires before the smoke gets too thick.

Optical alarms

Optical Alarms - where should they be used?

Optical sensors are more responsive to smouldering fires producing large particle smoke typical of fires involving furniture and bedding. They are more immune to invisible smoke produced by 'burning the toast' and similar cooking fumes. This makes them ideal for siting in hallways close to kitchens where false alarms from ionisation alarms may be a particular problem. The BS 5839: Pt.6: 2004 Standard recommends the use of optical alarms in circulation spaces of a dwelling, such as hallways and landings. Optical alarms are prone to false alarm if exposed to steam and should not be located too close to poorly ventilated bathrooms or shower rooms.

1. A light beam is pulsed in the sensor chamber every 10 seconds to ‘look’ for smoke. Any smoke present has to be visible to the naked eye so that the receptor can ‘see’ it. If no smoke is detected, the alarm will remain in a standby state.
2. When large particle smoke is detected, the light beam will be scattered onto the light receptor.
3. This will then send an electrical signal to the IC (Integrated Circuit).
4. If two consecutive signals are received by the IC, the alarm will sound.

For the best protection, you should install one of each. However, if you can’t have both, it’s still safer to have either one, rather than none at all.

Heat alarms

Heat Alarms - where should they be used?

Heat alarms are less likely to cause false alarm problems as they are not responsive to any type of smoke or fumes, only heat. Because of the potential for a slower response than smoke alarms, they should only be used in a fire alarm system that also includes smoke alarms, and all of the alarms must be interconnected. The BS 5839: Pt.6: 2004 recommends that heat alarms should be used in kitchens. It goes on to suggest that they may also have a role to play in the main living room but they should not be installed in circulation spaces or areas where fast response to fire is required.

REMEMBER -   False alarms are annoying but worst of all they give rise to a complacency culture.  Someone will say,"Oh it's only another false alarm".  One day they will be wrong!  So it's best to avoid false alarms and design your system accordingly.  Should you require advice regarding system design and installation please contact us.

British Standard Kitemark

Whichever type/model you choose, you should make sure that it meets British Standard 5446, Part 1 (BS 5446-1) and ideally also carries the British Standard Kitemark. 

The different models available

A lot of people do not check their smoke alarms until the battery becomes low and the unit starts to beep, so the best choice of power supply is usually the one that lasts longest.

Standard-battery alarms

An ‘ionisation battery alarm’ is the cheapest and most basic smoke alarm available and these are sold in most D-I-Y stores. An ‘optical battery alarm’ is a little more expensive and again sold in D-I-Y outlets.  Both types are powered by 9-volt batteries.

Battery alarms with an emergency light

These come fitted with an emergency light which comes on when the alarm is triggered. These are advised if someone in your house has hearing difficulties.

Alarms with 10 year Lithium Ion or Vandium Pentoxide Lithium batteries

These are more expensive, but you save on the cost of replacing batteries. They are available as ionisation, optical or heat alarms and are fitted with a long-life lithium ion battery or a sealed power pack that lasts for 10 years.

Mains-powered alarms

These are powered by your home’s electricity supply and need to be installed by a qualified electrician. A battery back-up is incorporated into the alarm panel so that the property remains protected in the event of a power cut.

Interconnecting or linked alarms

Some alarms can be connected to each other so that when one senses smoke, all the alarms in the property sound. They are useful for people with hearing difficulties and also in larger homes.

Alarms for people with hearing difficulties

Design requirements that should be considered to ensure an effective system

• Mains powered control panel with rechargeable battery back-up
• High intensity integral strobe light
• Auxiliary sockets for connection of additional optional strobe lights.
• Vibrating pad for placing under a pillow or mattrass
• Capability for interconnection throughout the alarm system
• Test button on control panel for testing the system
• Connections are monitored to check integrity of system
• Alarm clock input facility
• Remote trigger option
• Pager output facility