The following image is a commonly used infrared sensor:

It has an emitter and a receiver. The output can either be digital or analog. The emitter sends an infrared wave. Based on the object, it is reflected back and the signal is picked up by the receiver. Based on that, we know that we have something in close proximity.

There are multiple applications for infrared sensors:

• Detection of objects in close proximity
• Measuring temperature
• Infrared cameras
• Passive infrared for motion detection

The first was already discussed. The second one is the use of infrared detectors for detection of the infrared spectrum, and based on that, we calculate the temperature. Infrared cameras are widely used in the military, firefighting, and many places where we need to know from a distance that temperatures are high. The third one is the PIR. Passive infrared modules are used for motion detection and are used for automating homes.