Modular 3-piece design. With a superior electrical system and remote switch, REIN has always been upgradeable as subsequent generations are released. All parts of the 1st generation REIN are fully compatible with the 2nd and 3rd generation REIN; IPX-8 waterproof rating. Fully submersible to 100 feet for 24 hours. Fully-potted remote switch included; Strongest-in-class lens. The glass on the REIN is 3mm thick. It can take multiple hits from 5.56mm Simunition rounds, at contact-distance; Patented Battery Jack feature. This allows you to properly tension the battery inside the system to avoid battery bounce. This lengthens the life of your system and increases reliability substantially; Patented tail-cap cartridge is easily replaceable and allows for "clocking" so you can minimize cable exposure, without removing the tail of the light; The attached remote switch utilizes a cable exit from the tail cap that is perpendicular to the bore axis. This allows your cable to be protected from potential snags and impact; The patented remote switch, offers both momentary and constant-on functionality. The remote switch is electrically isolated from the push-button switch located on the tail cap; The proprietary remote switch offers unprecedented cable management possibilities never before available even with prior generation LCS units; Shockproof. Dustproof. The most durable weapon light made. Period