What is an example of a pyroelectric sensor?

The most common and widely recognized example of a pyroelectric sensor application is the Passive Infrared (PIR) motion detector. These devices are ubiquitous in security systems, automatic lighting controls, and presence detection applications. They don’t emit any radiation themselves (hence “passive”); instead, they detect the infrared energy naturally emitted by humans and animals.

Inside a typical PIR motion detector, there are usually two or more pyroelectric sensing elements arranged to detect differential changes. A segmented lens, often a Fresnel lens, focuses infrared energy from different zones within the monitored area onto these elements. When a warm body moves from one zone to another, it causes a sequential change in the infrared energy received by the elements. This differential signal (one element sees an increase while the other sees a decrease, or vice-versa) is amplified and processed to trigger an output signal, indicating motion.

While motion detection is the primary example, pyroelectric sensors are also used in other applications, such as non-contact temperature measurement (though thermopiles are often preferred here), flame detection (detecting the characteristic flicker frequency of flames), and gas analysis (measuring IR absorption at specific wavelengths).