How much

What are we talking about?

How long does it typically take to install a smoke alarm?

Typical time

Around an hour (mains). Battery alarms a few minutes

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Dependencies

Alarm types - see comments

Questions to ask

Type of alarm(s) required which depends on location. Battery (need replacing or 10 year) or mains powered with battery back up. See comments

Comments

There are two types of smoke alarms in general use:

• Ionisation: These are the lesser cost and most common. They are suitable for general and bedroom use and respond quickly to fast flaming fires as they detect the invisible parts of combustion gases. They will however alarm with particles given off by cooking so are not suitable for use in locations in or adjacent to kitchens.
• Optical (photoelectric): These cost a little more, detect larger particles of smoke and hence are more suitable for general use and near but not in kitchens as they are less prone to nuisance alarms. They are not so good at detecting fast flaming fires that give off little smoke.

Other alarms that will be found:

• Heat: These respond to heat only and can be used in kitchens and garages.
• Multi-sensor: these combine the ionisation and optical facility and have a higher level of tolerance to cooking fumes and steam
• Carbon monoxide: these are not smoke alarms. They may be used in addition to smoke alarms for detecting fumes from boilers and fires.

Some alarms have additional facilities, such as emergency lights and silence buttons, for use where false alarms can be a nuisance e.g. when cooking. Alarms specifically designed for the deaf are also available.

In a standard smoke alarm, the alkaline battery will need to be replaced every 12 months or so - the alarms usually emit a steady beep when the battery is low. Alarms fitted with 10 year lithium batteries are available. The advantage is that you don't have to replace the battery every year but the alarm has to be thrown away when the battery looses its charge.

Mains-powered alarms eliminate the problem of checking the battery but to be safe need a battery back-up and need to be installed by an electrician. They are typically fitted near a lighting ceiling rose which is used as the power source.

Many alarms are now interconnected, meaning that if one alarm is set off they all sound. In a 'new build' house or when rewiring an existing property a cable can be run between alarms to provide the interconnect. This is possible but not easy when fitting in an existing property - it usually results in exposed cable or trunking. To get over this problem radio bases are attached to each alarm so they can talk to each other wirelessly. These need mains power, usually from a lighting ceiling rose with the radio base and alarm being fitted nearby so cable can be run in the ceiling void. They also need built in battery back up.

Alarms that plugged into a light socket were available. They used a rechargeable battery which charged up when the light was turned on. The problem was that you need to make sure the light was turned on often enough so carried a degree of risk. They are seemingly no longer available.