The M4 Tactical Illuminator is compatible with S&W's SIGMA model "E" series. Snapping on or off the rail in under 2 seconds, makes the M-Series illuminators the first choice of individuals who want power AND performance in white light illumination. The instant-on/steady-on switch is a standard feature on this 6 volt powerhouse. The M4-Pro offers an optional safety switch and remote switch capability not included on the M4.