The Auto Tracer is made from high quality Aluminum, ball bearing quick detach, equipped with a sensor that will trigger an illumination device to light up internally when a 6mm projectile is fired. Tracer units require that you pair them with glow-in-the-dark / tracer Airsoft BBs for full effect. Tracer rounds are easy to follow in a dark night and make target acquisition much easier. The tracer will also work with regular BBs as a mock silencer or barrel extension, enhancing the look of your gun and BBs. Available with standard M4 / M16 birdcage flash hiders, easily to install and remove on the fly.