From now on, you can throw away those traditional bulky tracer units! Patented design from G&P, a strong blue LED inside the magazine illuminates 130 rounds BB continuously. The activate button is on the magazine top, so it turns on automatically when you load the magazine. Powered by 2 AAA or 3 N batteries (not included). Battery replacement is easy - just unscrew a small screw on the bottom of the magazine and you can access the battery compartment. A set of fresh batteries will last a long time since the internal LED is very energy efficient. Fits Marui M16 series. This smart and simple design is effective and brilliant (literally) and has received our RedWolf Innovation award!