1 What is an alarm detector?

Alarm detectors use sensors to sense various physical and chemical changes and generate signals such as currents and pulses to emit alarm signals.

2 What is a PIR motion sensor?

PIR motion sensors rely on passive absorption of infrared thermal energy for alarm, also known as thermal infrared detectors, and they do not emit infrared radiation by themselves.

3 Basic concepts of PIR motion sensors for infrared detection

Why can a PIR motion sensor generate an alarm signal when a person is moving within the alert area?

In nature, any object above absolute temperature (-273 ℃) will produce infrared spectra. The wavelength of infrared energy released by objects at different temperatures is different, so the infrared wavelength is related to the temperature.

There are two key components in PIR motion sensors:

• Pyroelectric infrared sensor (PIR): It transforms infrared signal (wavelengths between 8-12 μm) into electrical signals and has the ability to suppress white light signals in nature. In the alert area of the PIR motion sensor, when there is no human movement, the pyroelectric infrared sensor only senses the background temperature. When the human body enters the alert area, the difference signal between the human body temperature and the background temperature is sensed by the Fresnel lens and the pyroelectric infrared sensor. Therefore, the basic concept of infrared detection in PIR motion sensors is to sense the temperature difference between moving objects and background objects.
• Fresnel lens: There are two forms of Fresnel lens, namely refractive and reflective. Fresnel lenses have two functions. First, focusing, which refracts (reflects) the infrared signal emitted by the heat on the PIR. Second, it divides the alert area into several bright and dark areas, allowing moving objects entering the alert area to generate a variable infrared signal in the form of temperature changes on the PIR, which in turn generates a changing electrical signal.

4 What is the detection range?

The detection range refers to the normal sensing range of the detector, which means that the detector can detect the movement of all objects within this range and issue an alarm.

5 What is launch distance?

The farthest distance that the wireless device in the burglar alarm system can emit the wireless alarm signal in the form of electromagnetic waves after being triggered.

6 What is detection distance?

The maximum distance that an alarm detector can detect under normal operation.

7 What is induction sensitivity?

It refers to the distance of detection and the speed of response when an alarm detector is triggered. If the induction sensitivity is high, it can be detected at a long distance from the detector. If the induction sensitivity is low, it can only detect a relatively close range.

8 How to install a PIR motion sensor correctly?

Due to the fact that PIR motion sensors belong to weak signal detection equipment, attention must be paid to some details during installation, such as height, sensitivity, etc. To install a PIR motion sensor correctly, it is necessary to master the following aspects of information.

• First, it is necessary to understand the performance characteristics of the detector.
• Secondly, it is necessary to determine the installation location reasonably.
• Finally, careful debugging is necessary.

It cannot be said that it is installed correctly because it can send an alarm signal. How to determine the installation position of a PIR motion sensor?

(1) Determine the installation angle according to the manual

The installation height is not arbitrary, as it can affect the sensitivity of the detector and the effectiveness of preventing small pets. When the detector is installed at a height of 2 meters and 2.5 meters, the frequency of cutting the bright and dark areas it senses when a moving object passes through the ground is different.

(2) Don’t face glass doors and windows

The PIR motion sensor facing the glass doors and windows will have two problems: first, white light interference. Although PIR has a strong suppression function on white light, it is not 100% suppression after all. Therefore, avoiding facing glass doors and windows can avoid interference from strong light. The second is the interference of complex environments outside doors and windows, such as crowd flow and vehicles. Therefore, avoiding facing glass doors and windows can avoid interference from the complex environment outside the doors and windows.

(3) Don’t face hot and cold air vents or heat sources

The induction effect of PIR motion sensors is closely related to temperature changes. Both hot and cold air vents and hot and cold sources may cause false alarms in the detector. Some low performance detectors can also cause false alarms due to air convection through doors and windows.

(4) Pay attention to illegal intrusion routes

The purpose of installing detectors is to prevent illegal intrusion by criminals. Before determining the installation location, it is necessary to consider the main population of the building. In fact, we have prevented entry and exit, cut off illegal intrusion routes, and thus achieved our goal.

9 What is an active infrared detector?

The transmitting end actively emits infrared rays, while the receiving end receives infrared rays, forming a network of infrared rays. This type of detector can actively prevent intruders and avoid false alarms caused by the passage of small animals or the influence of climate, thereby minimizing the false alarm rate.

10 What are wired alarm detectors and wireless alarm detectors?

Alarm detectors can be divided into wired and wireless types based on the transmission method of alarm signals. After detecting an illegal intruder, the alarm detector transmits the alarm signal to the alarm control panel in two ways. Wired alarm detectors transmit alarm signals by the switch signal or level signal. Wireless alarm detectors transmit alarm signals by emitting electromagnetic waves of a certain frequency.

11 Advantages and disadvantages of wired alarm detectors and wireless alarm detectors

(1) Advantages and disadvantages of wired alarm detectors

• Advantages: The transmission of alarm signals is relatively stable and not easily affected by external factors.
• Disadvantages: Affecting aesthetics, requiring a large construction workload, complex operation, and inconvenient maintenance, requiring dedicated personnel for maintenance.

(2) Advantages and disadvantages of wireless alarm detectors

• Advantages: It will not damage the overall appearance of the prevention area, is easy to install and operate, and is easy for the elderly and children to learn.
• Disadvantage: The alarm signal may be affected by external factors, resulting in a attenuation of the transmission distance of the alarm signal.