PIR (Passive infrared) sensors usually require infrared lenses to work properly.

A PIR sensor is a type of sensor used to detect a human body or other heat source, which works by measuring the temperature difference between the target object and its surroundings. However, the detection range of the PIR sensor is usually relatively wide, and if the infrared lens is not used, it may misalarm or miss the presence of the target object.

The infrared lens can reduce the detection range of the PIR sensor and improve its accuracy and reliability. In addition, infrared lenses can also reduce the impact of other interfering factors on the sensor, such as background noise, light, and so on.

Therefore, in order to ensure the normal operation of PIR sensors and improve their performance, it is usually necessary to match infrared lenses.