Detecting infrared radiation. Everything above absolute zero emits infrared radiation, which is also perceived as heat in the far infrared (FIR) range. In normal environments, people and animals emit more infrared than their surroundings, and infrared night vision systems are used to detect objects not easily visible to the naked eye. See
infrared.
Night Vision
Increasingly found in luxury automobiles and also available for aftermarket installation, infrared night vision systems let people see distant objects that would otherwise be invisible. (Image courtesy of FLIR Systems.)