Infrared sensors are commonly used to measure distance and proximity of objects. As there is no contact and no visible light these sensors are an unobtrusive way to detect obstacles.
Range finding sensors use a beam of infrared light to determine the distance from the sensor to the object. Ideally suited to indoor use these sensors often include compensation for infrared interference from other sources like the sun and indoor lights although direct sun outdoors can be a challenge.
Proximity infrared sensors also emit a beam of infrared light but use the level of reflected light to determine if an object is within a range or not. They indicate yes or no, rather than how far.
Other infrared sensors can detect infrared light as a measure of temperature, PIR sensors include extra logic to detect motion and infrared signal receivers know what your television remote is up to.
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