Alarm Systems - Are They Safe?

If there is one thing in this world, one benefit of modern life you tell yourself, its the reliable sentry always looking out for your and your loved ones' wellbeing, the sentinel at the ramparts, it is the good old alarm system. Upon noticing the little lights twinkling away in the corner of a room it is often with a feeling of satisfaction and reassurance that one is doing all that can be reasonably expected to safeguard ones home and every thing of value in it. You dutifully always set the alarm when you go out, it rarely gives a false positive and it protects you from fire, intruders and villains of all descriptions. Oh, and may be a condition of your or your landlord's insurance policy.

But is it safe? "Oh Yes," you say. "We always put it on when we go out."

Technical: There are three main components in most wired domestic alarm systems:

1, The Systems Board, 2, The Control Panel / Keypad and 3, the various Sensors (fire, smoke, CO2, glass, intruder, flood etc.) Some systems are linked by phone line or mobile SIM Card to a 'Central Office' staffed 24/7 by responders who take action according to the instructions associated with the address. Other systems merely activate a sounder(s) and strobe(s) but some when tripped do both. Some are linked to a pendant worn around the neck.

1.    The Systems Board is mains powered through a sealed 12v battery and delivers Direct Current to the sensors which are themselves stand-alone mini-computers. In the normal course of events the whole alarm system is controlled by a remote keypad, usually situated somewhere near the main entrance. Operation is simple, reliable and robust. The Systems Board is usually tucked away in a cabinet somewhere inconspicuous such as under the stairs or in the eaves and is rarely given a second thought. Its circuits however may produce significant oscillating magnetic fields over a range of metre or more. If for example it happens to be the other side of a partition to a child's bed or desk, a favourite / TV chair or near a pets sleeping place, serious damage to health can occur over time.

2.    The Control Panel / Keypad: Should a circuit be broken for any reason, the alarm is set off. The panel then indicates which sensor or zone of sensors has been triggered. The Panel like the Systems Board may, perhaps due to conversions or modifications to the use of space, be mounted inappropriately close to areas where people or pets spend a lot of time.

3.    The Sensors: The range of alarm sensor types is vast and varies from such things as panic buttons, under-mat pressure pads, ultrasound glass breakage sensors, radioactive and optical smoke sensors and many others. Motion sensors are usually contained within the familiar little white enclosures typically mounted in top corners of rooms, passageways, garages etc. Their internal construction generally falls into three types (PIR, Dual-Tech, Tri-Tech) and all three types work by breaking the circuit back to the Systems Board when the type of event they are designed to detect occurs.

PIR - Passive Infra Red: These are an early type of motion sensor that picks up moving heat signatures through a little frosted window and whilst being cheap and readily available are subject to poor event discrimination and in the past at least, frequently produced false alarms. They are however the most environmentally friendly.

Dual Tech: To overcome false alarms Ultrasound was added. It fills the room space with 'silent' standing waves and listens for the Doppler frequency shift caused by any moving object. Some sensors only produce this form of radiation when the PIR has been triggered but others may produce it 24/7. Being constantly bathed in ultrasound even if only when you move is liable to affect hearing, produce tinnitus, upset sleep and may have many other side-effects not immediately associated with alarm systems.

Tri-Tech: To make motion / intruder alarm sensors even more reliable and even less prone to false alarms, Microwave Radiation capabilities have been added. These detect Doppler shift in a similar way to Ultrasound and like Dual-Tech sensors may invoke the Tri-Tech 10 GHz. microwave signal only when the other two sensors agree that an alarm event is occurring. Or they may fill the space 24/7 but, as with Ultrasound the health consequences can be broad-ranging and are rarely linked to alarm sensors. The power output of the microwave component generally has three levels according to the volume of the space being protected. Low, Medium or High and is set by the installation engineer (who must disable the Systems Board when setting up the sensors in order not to be blasted in the face by the microwave and ultrasound signals as the sensor cover is replaced).

Most homeowners do not understand that deactivating their alarm system when they return home simply tells the system not to raise an alarm when sensors are triggered. It does not cease the sensor operation. They continue to operate 24/7. This mode of operating is chosen because it makes the sensors more reliable and stops them suffering condensation and corrosion when unpowered. It does however subject occupants to a never-ending stream of radiation as they move about in their living space. Being hit by a bolt of ultrasound, swiftly followed by a bolt of microwave radiation upon entering a room may alert residents to an issue. By leaving the sensors running 24/7 there is less likelihood that any association will be made. This article focusses on domestic alarm systems but many of the concerns expressed here apply equally to nursing / care homes, offices, factories and other alarm-protected enclosed spaces.

Motion sensors may be fitted with visible indicator lights (red, green, orange, blue) that are tripped by movement and generally indicate the sensor is detecting and discriminating as it should. A blue indicator light may suggest a microwave / Tri-Tech sensor and if this is the case, it is probably a job for the professionals. Ultrasound can be detected by a relatively cheap 'Bat Detector' but the 10 GHz. radio frequency (RF / microwave) radiation is above the range most readily available / affordable meters can detect. To establish what kind of sensors you have see 1. the installers notes / invoice, 2, by calling the alarm service provider or 3, by having an alarm engineer come and deactivate the Systems Board so as to physically examine the motion sensors.

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