Infantry troops have enthusiastically taken to night vision gear. Now they are getting thermal imaging sights as well. The Enhanced Night Vision Goggle (ENVG) has been in development for several years, and now three different prototypes are being field tested by troops. American tanks have had thermal imaging sights for over a decade and they have been very effective, and popular. Thermal imaging sights see changes in temperature. Thus people (or animals), vehicle engines and the hot barrels of weapons that have been fired several times, will show up clearly, especially in cold weather, or at night. This enables troops to see through fog, or even sand storms. The ENVG were not possible until the weight, and cost, of the necessary electronics came down. Even so, the ENVG will cost 2-3 times what the current night vision goggles the troops use cost (about $4,000 for one that covers one eye). Two vexing problems are weight and battery life. Getting the weight under two pounds is less of a problem than getting battery life to 40-50 hours (which is standard for current NVGs). Fuel cell technology is just now entering commercial use, and the ENVG developers are looking to that for a longer lasting, lightweight energy source. 

The Special Forces already have a binocular ENVG (the PVS-21) that weighs 1.67 pounds and uses an infrared light system to provide limited vision in areas (like caves and inside darkened buildings) where there is no light to intensify. But a true ENVG, like the ones being tested, have passive "total blackout" vision relying on heat sensing, not tiny infrared spotlights (that cannot be seen without special glasses, which are built into the PVS-21).