Smoke particles change the balance of the current. When this happens a signal is sent to the integrated circuit and the alarm sounds. Wireless devices communicate with each other and other devices without the use of connecting wires. This can be through interlinking by radio or through wi-fi. Interlinked smoke alarms will use the same optical or ionisation technology mentioned above, so, they're not a type of alarm in their own right. Pros: Can suit dustier areas, such as lofts, the area near your bathroom or rooms where people smoke. Interlinking when one alarm goes off, all the connected detectors are activated. This can be particularly useful in a larger house.

In Scotland, since February 2022, interlinked smoke and heat alarms have needed to be fitted in all homes.You can put them in kitchens and garages because they’re not prone to false alarms from cooking or exhaust fumes. But they are slower to respond than smoke alarms. Some smart models sound an alarm on your smartphone and through the alarm itself when triggered – this is the most helpful kind of smart alarm. As of February 2022, the Nest protect smoke and CO alarm no longer meet the requirements of the new Scottish alarm laws. This is because, while it can be linked to other Nest alarms, it has no way of detecting heat rises or of being linked to another heat alarm.

So if you’re out of your home and not near your phone when the messages come through, you’ll have no way of knowing the alarm was sounding.Smart smoke alarms are designed to sound the alarm when they detect smoke, as a conventional smoke alarm would. But the unique selling point of a smart smoke alarm is the ability to send alerts to your phone when there’s a fire. Heat (thermal) alarms detect heat (hot air) instead of smoke. The alarm is triggered when the temperature within the sensor chamber reaches over 58 degrees Celsius – generally when a fire is well established.