Thermal infrared imaging cameras are available for a wide variety of uses. Federal sensors offers Infrared IR cameras for 
the following applications;

Military thermal imaging for remote sensing, weapon sighting, perimeter security, installation surveillance & force protection
Thermography ir imaging for predictive maintenance, electrical, mechanical, and overall preventive maintenance
Research and development imaging for circuit boards, IC, PBC, and a wide array of specialized applications

Thermal infrared imagers are detector and lens combinations that give a visual representation of infrared energy emitted by all objects above 0 k.  In other words thermal imagers let you "see" heat. Depending on the
sophistication of your system thermography is capable of providing very detailed images of situations invisible to the naked eye.

 Thermal images cannot see through walls, although you can gather much information about the inside of the wall as well as what is happening on the other side of the wall.
For example you would not be able to see people and plants involved in an illicit indoor growing operation from the outside of the building. You would be able to see and monitor the heat escaping from the building that would be a telltale sign of an indoor growing operation. Click here for legal cases involving thermal infrared for narcotics detection

 You would also be able to see things like studs inside the walls, or damaged insulation in roofing applications.   We hope that dispels a few of the most common myths regarding infrared energy. Thermal imagers in Hollywood and in real life are very different.  The remainder of this paper will focus on the real life thermal imagers and how they work.

Thermal energy is transmitted in the infrared wavelength ( 1 micron to 100 microns ). You can see by the image above that thermal energy is closely related to visible light in that it travels in a wave. The human eye can only see the narrow middle band of visible light that encompasses all the colors of light in the rainbow. Thermal infrared imagers translate the energy transmitted in the infrared wavelength into data that can be processed into a visible light spectrum video display. Visible light is dependent on a light source ( the sun or artificial ) reflecting off an object to be received by our eyes. Remember, all objects above 0 degrees Kelvin emit thermal infrared energy so thermal imagers can passively see all objects regardless of ambient light. This can give you an enormous advantage. Thermal infrared imaging performs in a wider range of environments than other night vision technologies. Additionally, IR devices can serve your inspection needs at night or in broad daylight.

Most objects in natural scenes, as well as human beings and manmade objects, emit electro-magnetic radiation in the form of heat. Thermal imagers or infrared viewers (also known as FLIRs) gather the infrared radiation and form an electronic image for the operator of the infrared thermal camera.  Since they do not rely on reflected ambient light, thermal imagers are totally light-level independent. They also have significant penetration capabilities through obscurants such as fogs, hazes, and conventional battlefield smokes. 

Thermal Imagers (FLIRS)
Thermal imagers, sometimes called FLIRs (forward looking infrared), rely on thermal contrasts to generate a video image. FLIRs are true thermal imaging devices that create pictures based on heat energy emitted by the viewed scene rather than by light reflected off of it. Heat in the infrared region of the electromagnetic spectrum behaves like visible light and can be optically focused and collected. FLIRs employ various materials whose electrical properties change when heated to perform the transformation from infrared energy to electronic signal levels. These changing signal levels are translated into video signals in which a different shade of gray on the TV monitor is assigned for each detectable temperature level. Because the energy being sensed is heat and not light, FLIRs are totally unaffected by the amount of light in a scene.