Magnet Reed Contacts – Often used in homes on doors. Basically these involve two metal strips which, when they come together, complete a circuit. When the door is opened the circuit is broken and the alarm is activated.

PIRs (Passive Infra Red Movement Detectors) – Mainly used in domestic or office settings and positioned high up (usually in corners) to detect movement. They can spot the difference between humans and other intruders – such as mice – to avoid false alarms.

Dual Technology Movement Detectors – These combine infra red and microwave technologies. Both have to be activated making false alarms very unlikely.

Vibration Detectors – Normally fitted to door or window frames. They detect high and low frequency vibration and can be adjusted to suit local conditions.

BGDs (Break Glass Detectors) – Usually fitted over or next to shop fronts. They detect the sound of breaking glass and any accompanying change in air pressure.

Infra Red Beams – You’ll have seen these in the movies! Thin beams of light that trigger an alarm when broken. Dual or twin beam units are sometimes used – both have to be interrupted to set off the alarm. They can be used inside or outside.

PA (Personal Attack) Buttons – Units with two buttons that must be pressed at the same time to activate an alarm. They can sound an audible alarm, or silently alert an ARC (Alarm Receiving Centre) – a place where remote monitoring is provided by the security system provider.