system
Given the following post, respond as if you're commenting on Reddit:
human
How the heck does a laser/infrared thermometer actually work?

The way a low-tech contact thermometer works is pretty intuitive, but how can some type of light output detect surface temperature and feed it back to the source in a laser/infrared thermometer?

Edit: 🤯 thanks to everyone for the informative comments and helping to demystify this concept!
gpt
Imagine you're a master blacksmith. You have to heat up your iron to the right temperature to work with it. Too hot and it turns to pure liquid. Too cold and it won't bend when you hammer it. Once you've been doing it long enough, you can probably tell the temperature pretty accurately based on exactly the color of the red-hot glow, right?

Well, all objects are glowing just like hot metal does. It's just that most objects aren't hot enough that the glow is in the visible spectrum. You glow in infrared, which is slightly lower energy than red. This is also how thermal cameras work.

The thermometer can measure how much you're glowing in infrared, and just like the blacksmith, can tell your temperature.

The laser is just a thing for you to use to know where it's measuring, to aim. It's just like a laser-mounted gun sight.