You may not know it, buy your body is giving off heat rays. So is everything else around you. The strength of these rays, which are also known as infrared rays, depends on how warm or cold things are.
Special cameras and instruments can pick up these heat rays and turn them into pictures. In this way, it is possible to detect and see things in complete darkness. Some burglar alarms work in this way, and so do night sights used on guns. It’s also possible to take heat pictures of objects that show how hot or cold various parts of them are. This is very useful in finding out where heat is escaping from a building, for example, or if a part of the body is unusually hot or cold.
After the earthquake in Mexico City in 1985, these special instruments were used to locate survivors buried in the rubble.