The U.S. Marine Corps is testing a clip on electronic IFF (Identify, Friend or Foe) device for M-16 rifles. If troops are operating in an environment (at night, in an urban area) where there's greater potential for friendly fire incidents, the device lowers the danger level. A marine seeing someone who could be friend or foe, merely presses a button on the IFF device and, if a low level light glows red, knows that the other guy also has one of these IFF devices with the proper code. If the green light goes on, the other guy is either hostile, or a marine without an IFF device, or with a broken one. Either way, it takes some of the stress out of night operations in confused situations. The devices can be set with new IFF codes, or programmed to send the code for only a set time (in hours) in case there's risk that the enemy might get weapons off dead marines. The device is expensive, the marines won't say how expensive, and is still being evaluated.