IR Motion Sensor, what is it "looking" for?

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IR Motion Sensor,

What is IR "looking" for?

I have an IR motion sensor controlling my garage outdoor lights. Currently it's just a no frills, non-smart home setup.

What are IR sensors looking for? It detects me walking up the driveway. It will detect my neighbor's cat. And during heavy rain the lights stay on.

But when I drive my car up the driveway it does not detect my car and it's hot engine.

So what is an IR sensor "looking" for?

Thanks!

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Per chatGPT as I figured it would me more detailed that what I would cobble together:
IR (infrared) motion detectors primarily look for changes in infrared radiation, which is emitted by objects based on their temperature. These detectors typically work by sensing the movement of warm bodies, like humans or animals, in their detection range.

There are two common types of IR motion detectors:

  1. Active IR Detectors: These emit infrared light (usually in the form of a beam or grid) and measure the reflection or interruption of the light. If the beam is broken or the pattern is disturbed, the sensor detects motion.

  2. Passive IR (PIR) Detectors: These do not emit infrared light but instead detect infrared radiation emitted naturally by warm objects, like a human body. When a person or animal moves in the detection zone, it changes the heat signature in the field of view of the detector, triggering an alarm or action.

Essentially, these detectors are sensitive to heat changes and the movement of objects that emit or reflect infrared radiation.

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Most likely, PIR sensors filter out signals from objects that are “too hot“. Thus, a human body would be sensed, but not a hot automobile engine.

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I wonder, is that observation from experience? I cannot speak to that because we have an EV. However, our Outdoor Hue motion sensor detects our car from about 15 feet away when it pulls into the driveway, any time of the year.

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The key is the temperature difference. The engine is surrounded by a metal enclosure (usually) that may be close to the outdoor temperature if the sun isn’t shining. Just like how it takes longer for a motion sensor to “see” you when you’re wearing a winter jacket and hat.

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That’s why I was curious. I don’t have an engine. But there is heat from the battery cooling and heat pump, just nowhere near the amount generated by an ICE vehicle.