How do passive infrared sensors work?

How do passive infrared sensors work?

• A. Reads the heat of people to activate
• B. Measures ambient light level
• C. Detects sound
• D. Measures air quality

Answer: (A)

Passive infrared sensors work by sensing changes in infrared radiation, the heat energy, in their field of view. Inside, a pyroelectric element is arranged to respond to differences between two sensing areas. When a warm body, like a person, moves across the view, the infrared energy hitting each area changes, creating a differential signal. The sensor’s electronics amplify this change and trigger the output when the difference crosses a threshold, turning on lights or activating a switch. The “passive” part means the sensor doesn’t emit any energy itself; it simply detects energy that’s already radiated by people and objects. A lens or optical cover is often used to split the view into zones so movement across the scene produces a detectable change. This is why the idea that it reads heat from people to activate is the best description. It isn’t about ambient light, sound, or air quality, which these sensors do not monitor.

Passive infrared sensors work by sensing changes in infrared radiation, the heat energy, in their field of view. Inside, a pyroelectric element is arranged to respond to differences between two sensing areas. When a warm body, like a person, moves across the view, the infrared energy hitting each area changes, creating a differential signal. The sensor’s electronics amplify this change and trigger the output when the difference crosses a threshold, turning on lights or activating a switch. The “passive” part means the sensor doesn’t emit any energy itself; it simply detects energy that’s already radiated by people and objects. A lens or optical cover is often used to split the view into zones so movement across the scene produces a detectable change. This is why the idea that it reads heat from people to activate is the best description. It isn’t about ambient light, sound, or air quality, which these sensors do not monitor.