This is a LaserMax Laser known as the Hi-Brite, model LMS-1141P.
Designed specifically for use in Glock 17" 22" 31" and 37 pistols" the LMS-1141P replaces Glock's factory spring guide assembly with a high intensity red laser sighting system for advanced target acquisition. Easily user installed without the need for gunsmithing or special tools" the Guide Rod Laser is constructed with rugged" precision components including aircraft-grade aluminum and genuine Wolff springs.
Features:
Pulses for superior visibility and faster identification
Internal design does not restrict grip or holster selection
Ambi on/off switch