This is a Crimson Trace Corporation Laserguard known as the Laserguard, model LG-489G.
The LG-489G is a seamlessly integrated green laser sight for Smith & Wesson's M&P Shield 9mm and .40 S&W concealed carry pistol. This Laserguard(R) is designed to match the unique design of the pistol" and features Instinctive Activation(TM) - meaning the laser is activated when the gun is held in a natural firing grip. Quickly installed with no gunsmithing required" the LG-489G is also fully adjustable for windage and elevation. Features a powerful green laser diode for improved laser targeting in all lighting conditions.
Features:
Front activation
Green laser
Factory sighted at 50Ft
.5 inch diameter at 50 feet