These kind of alarms are exactly what they say they are; a heat sensitive alarm. This means they don't respond to smoke, only heat and so you should also include smoke alarms in the home or office.
Heat alarms are usually used in situations where smoke, dust and cooking fumes are present and would set off a smoke alarm.
When the internal sensor feels heat above 58 degrees celcius it sets of the alarm.
All Fire Safety Equipments heat alarms are BS Kitemarked and manufactured in the UK for your piece of mind.
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Gas Alarms : http://www.gosgoo.com/showroom/detector/