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Reasons & Solutions of False Alarm -- Burglar Alarm System

May 24, 2018

Reasons & Solutions of False Alarm -- Burglar Alarm System

The wireless detector's anti-jamming capability shows that the same-frequency interference is likely to cause false alarm and failure alarm. Infrared detectors are inaccurate in judgment of intrusion behavior and cause false alarm. Infrared detectors are susceptible to false alarms due to environmental factors such as temperature and light. The power supply system of the wireless detector lacks power. When the power is low, there is no effective information transmission so that the detection distance of the detector becomes shorter or it does not work, resulting in missed false alarms. Because the host and the detector are all set by wireless encoding, there is repetition of the host and detector re-encoding result in false alarms.

1. False alarm due to improper system design

Equipment selection is the key to the system design. There are a wide variety of alarm systems. Each has its own characteristics, application scope and limitations. Improper selection can cause false alarms. For example, the use of vibration detectors near the vibration source (airfield and railroad) can easily cause false alarms in the system. The use of ultrasonic detectors in places where bats often appear can also cause false alarms. This is because bats emit ultrasonic waves; High-frequency sounds such as electric bell and metal impact can cause false alarms for single-technology glass break detectors. Therefore, to reduce false alarms caused by improper equipment selection, system designers must be familiar with the principles and characteristics of various alarm devices. , scope of application and limitations. At the same time, we must also grasp the on-site environmental conditions, climate conditions, electromagnetic field strength, and changes in illuminance in order to select alarm equipment according to local conditions.

In addition to the selection of equipment, the improper design of the system also manifests itself in the equipment installation location, installation angle, protective measures and system wiring. For example, when a passive infrared intrusion detector is installed facing an air conditioner or ventilation fan, it will cause a false alarm of the system; if an active outdoor infrared detector is not used for proper sun protection (the sun shield is also best for protection), it is bound to cause false alarms; alarm lines and power lines, lighting lines and other strong electric circuit spacing is less than 1.5m, and without adding anti-electromagnetic interference measures, the system will also generate false alarms.

2. False alarm caused by improper construction

This part of the problem is mainly manifested in the following aspects:

(1) No strict construction according to design requirements.

(2) Improperly installation equipment or improper inclination.

(3) Solder joints are fused, burr, or improperly shielded measures.

(4) The sensitivity of the device is poorly adjusted.

(5) Inspection equipment for construction does not meet the measurement requirements.

The solution to the above problems is to strengthen the supervision and management of the construction process and implement the safety supervision system as soon as possible. This will help improve the quality of the project and reduce the number of false alarms caused by the construction process.

3. False alarm caused by improper use of the user

Improper user use often causes false alarms in the alarm system. For example, the window with the door magnetic was not close well, and it was blown away by the wind at night; the staff strayed into the arming zone; the alarm system was accidentally triggered; the system check-in personnel misoperation; the change of the work procedure was not observed, etc. To analyze the user's improper use, find out where the error is, and improve the user's level, can greatly reduce the number of false alarms in the alarm system.

4. False alarm caused by environmental interference

The false alarm caused by the environmental interference refers to the alarm system being generated under normal working conditions. It is unavoidable from the principle, but the facts are not needed and it belongs to false alarm. For example, thermal airflow causes false alarms from passive infrared intrusion detectors; high-frequency sounds cause false alarms from single-technology glass break detectors; and ultrasonic sources cause false alarms from ultrasonic sensors. The most effective measure to reduce such false alarm is to use dual-detector detectors (two different principle sensors detect the “target” at the same time, and the alarm device only sends an alarm signal). The current products include: microwave-passive infrared detector, voice-activated glass broken detector, ultrasonic-passive infrared detector and so on. However, some environmental noise detectors can't do anything, such as: rats infestation areas; pets walking indoors. To this end, scientists and technicians have introduced micro-processing technology into the alarm system to enable them to have a certain ability to discriminate and think, and to judge, to some extent, whether it is an intruder or an alarm caused by environmental noise.


To reduce false alarms, it is indispensable to proceed from the aspect of human action. The establishment of alarm information confirmation mechanism can reduce the number of alarms. After the alarm center receives the alarm information, it should send a confirmation signal to the alarm host to indicate that the center has received it, and the alarm host should resend it when it does not receive the confirmation signal. In terms of technology, alarm signals can be confirmed by various means at present. For example, multiple detectors (commonly used by dual infrared + infrared plus microwave) are installed. When multiple probes detect an intruder signal at the same time, they send alarm signal to the host. By this we can reduce false alarm rate.