A number of everyday objects work off of lasers, some visible, some not. Many digital cameras use infrared light to focus, touchless thermometers use light to gauge temperature, and a standard computer mouse uses a laser to detect your movement of it, and from that, change the position of the pointer on your computer’s monitor.
To start, the office mouse. Older mice used to use a roller ball detector in place of the laser – this relied on good friction between the desk and the mouse to actually move the ball in its socket, and since a lot of desks are smooth wood, a mousepad was soon a common fixture. Other options included a thumb roller ball, which moved the cursor without asking the user to move their wrist, or pure keyboard interfacing.
There were drawbacks. The biggest one was that the mouse wouldn’t work if it couldn’t roll, and having a physical object that could become jammed or clogged, or perhaps too worn down to rotate in certain directions could get in the way of the person using it. While optical mice are not totally immune to physical problems, the light at least can’t be literally worn down by use.
Now, mice rely on a combination of an LED and a sensor inside the body of the mouse to do the moving. Light bounces off of the surface and back into the cavity, where the sensor can compare the information received right before and tell if the surface underneath the mouse has changed at all. It’s remarkably complex for such a small, common object.
Next, infrared thermometers. Infrared light is outside of the wavelengths humans can see, but some other animals can identify if an object is hot or cold just by looking at it. Where metal only appears to glow to us when it is far, far too hot to touch, a snake might observe that it starts to glow when it reaches the temperature of the average field mouse. Infrared light is actually bouncing all around us, all the time, and the infrared thermometer is simply translating an invisible force into a number with a specialized sensor and a lens to focus it onto said sensor! For this reason, infrared thermometers can only measure the surface of an object; it’s like it’s telling you what the color of the outside is. A metal stick thermometer works in much the same way, but because of the probe, it’s able to ‘see’ the inside of the object being measured.
And then there’s auto-focusing cameras. If you’ve been shopping for a camera, you’ll notice that some autofocus, and some do not. Meanwhile, most phone cameras autofocus unless you specifically turn that setting off. Active autofocus on cameras uses an infrared beam to bounce off of a subject and identify how far away it is to give the best focus. This is why your phone or camera will seem to oscillate between two objects near the center of the picture’s field – it’s likely hitting both with the focusing laser, and having a hard time identifying which one you mean to focus on. It’s also why you may have to switch to manual focus for objects that are more than twenty feet away, as that’s about where the laser’s range caps out.
This is why certain cameras are forbidden out in the field during military exercises – when they try to focus, it’s possible to see those lasers in night-vision and infrared cameras, which makes the person using the camera very visible, even from a great distance. Highlighting your spot with light only the opponent can see is not ideal. Some insect photographers find the focusing light distracts their subject, because bug eyes are attuned to different wavelengths of light, and otherwise invisible lights to us read like car headlights to their eyes.
Sources: https://computer.howstuffworks.com/mouse4.htm
https://www.tamron.com/global/consumer/sp/impression/detail/article-what-is-autofocus.html
