The U.S. Army and Marines are testing BTID (Battlefield Target Identification Device), an IFF (Identify, Friend of Foe) device for ground combat. Since World War II, warplanes have used IFF, which in aircraft is a special radio that, when it receives an interrogation signal, transmits a special code. If its the right code, the anti-aircraft weapons, or approaching fighters, will know it is friendly and not fire. IFF for ground combat vehicles has been suggested before, but never acted on because of the expense, and the lack of numerous friendly fire incidents. But since the 1991 Gulf War, that attitude has changed. Better American anti-tank weapons, operating at longer ranges, has made friendly fire more of a problem. 

Currently, IFF is handled with Combat Identification Panels (CIP0 which are 24 x 30-inch panels that resist absorbing chemical weapons and are covered with a high reflectivity tape. CIPs will show up distinctly when viewed through FLIR (Infrared radar favored by aircraft) or thermal sights (used in armored vehicles). The CIP panels cost about $240 each, and you need five for a tank and three for most other armored vehicles. The use of CIPs prevented a lot of friendly fire in 2003, as did two other simple measures. For night operations, when American troops are using night vision goggles, unarmored vehicles were equipped with Phoenix Junior lights. These flash every two seconds, but at such a low level, you can only see them through night vision goggles. Phoenix Junior lights cost $25 each, and sometimes infantry wore them as well, if there was a chance of friendly fire during a night operation. And then theres Glo-Tape, which glow at night when viewed through night vision goggles. Each inch square piece of tape costs fifty cents, and each soldier wears four of them, two on the helmet and one on each shoulder. 

But in Iraq, the CIPs tended to get covered in the fine dust, and become useless unless constantly washed. The Phoenix Junior lights did not show up in the thermal sights that tanks and other armored vehicles used. So the army developed BTID. While more expensive than CIPs, dust wont be a problem, and you can install just the transmitter in many non-combat vehicles traveling with a combat unit. This makes them not much more expensive than CIPs. The armys major problem will be getting the air force and navy to equip their warplanes with BTID transmitters (which have a range of about five kilometers). BTID is not considered the last word in anti-fratricide (friendly fire) devices. Ultimately, the army and marines want every soldier to carry some kind of  electronic device that will tell friendly weapons and commanders where they should not be firing.