system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do those infrared thermometers work? How does flashing a red light on someones head give you their body temperature?
gpt
The red dot is just a laser targeting tool, allowing you to easily see what you are measuring the temperature of.

They work by having a sensor that detects infra-red light. Everything gives off light, it is just that unless they are really hot, that light is too low in energy for us to see - it is infra (that is, below) red light. You can feel this, however, because it still shines on your skin, and is able to warm it up.

The sensor detects the amount of a certain 'colour' of infra-red light that is being given off, and the hotter something is, the more light it gives off. From that, the computer inside the device can calculate and display a temperature.