This is a continuation of our previous article What is a Burglar Alarm (part 1) and discusses the various devices available. If you need any advice and are based in Essex or Hertfordshire, please give us a call and we will be happy to help.

Sensor types

The passive infrared detector (PIR) is one of the most common detectors found in household and small business environments because it offers affordable and reliable functionality. The term passive means the detector is able to function without the need to generate and radiate its own energy (unlike ultrasonic and microwave volumetric intrusion detectors that are “active” in operation). PIRs are able to distinguish if an infrared emitting object is present by first learning the ambient temperature of the monitored space and then detecting a change in the temperature caused by the presence of an object. Using the principle of differentiation, which is a check of presence or non-presence, PIRs verify if an intruder or object is actually there. Creating individual zones of detection where each zone comprises one or more layers can achieve differentiation. Between the zones there are areas of no sensitivity (dead zones) that are used by the sensor for comparison. Ask us if you want to see examples of our installations in Essex and Hertfordshire.

Microwave detectors

This device emits microwaves from a transmitter and detects any reflected microwaves or reduction in beam intensity using a receiver. The transmitter and receiver are usually combined inside a single housing (monostatic) for indoor applications, and separate housings (bistatic) for outdoor applications. To reduce false alarms this type of detector is usually combined with a passive infrared detector or “Dualtec” alarm.

Glass break detectors

The glass break detector Burglar Alarm System may be used for internal perimeter building protection. When glass breaks it generates sound in a wide band of frequencies. These can range from infrasonic, which is below 20 hertz (Hz) and cannot be heard by the human ear, through the audio band from 20 Hz to 20 kHz, which humans can hear, right up to ultrasonic, which is above 20 kHz and again cannot be heard. Glass break acoustic detectors are mounted in close proximity to the glass panes and listen for sound frequencies associated with glass breaking. Seismic glass break detectors are different in that they are installed on the glass pane. When glass breaks it produces specific shock frequencies which travel through the glass and often through the window frame and the surrounding walls and ceiling. Typically, the most intense frequencies generated are between 3 and 5 kHz, depending on the type of glass and the presence of a plastic interlayer. Seismic glass break detectors “feel” these shock frequencies and in turn generate an alarm condition.

Smoke, heat, and carbon monoxide detectors

Most systems may also be equipped with smoke, heat, and/or carbon monoxide detectors. These are also known as 24 hour zones (which are on at all times). Smoke detectors and heat detectors protect from the risk of fire and carbon monoxide detectors protect from the risk of carbon monoxide. Although an intruder alarm panel may also have these detectors connected, it may not meet all the local fire code requirements of a fire alarm system. If you aren’t sure which type of system you need, then our Essex and Hertfordshire based specialists can help advise you as to which would be best for you.

Vibration (shaker) or inertia sensors

These Burglar Alarm systems are mounted on barriers and are used primarily to detect an attack on the structure itself. The technology relies on an unstable mechanical configuration that forms part of the electrical circuit. When movement or vibration occurs, the unstable portion of the circuit moves and breaks the current flow, which produces an alarm. The technology of the devices varies and can be sensitive to different levels of vibration. The medium transmitting the vibration must be correctly selected for the specific sensor as they are best suited to different types of structures and configurations.

Door / Window Contacts

These Burglar Alarm devices are mounted on the frame of the door with a magnet on the door itself, and detect the door being opened typically more than 10mm. They can be used on a door in order to start an entry timer on the system to allow unsetting, or to cause a system to set when leaving a property. Alternatively there can be an instant alarm on a door or window if it opened when the system is set. Get in touch to find out more if you are in or around Essex and Hertfordshire.