One of the more contentious issues with laser sights is the activation. Some come on instantly, while others require the user to press a button or slide a toggle switch. Both methods have their advantages and disadvantages, with the best system determined by the user's preference.
Viridian Green Laser came up with a novel solution: Have the laser come on instantly when drawn from the holster. To that end, they partnered with various holster manufacturers to create holsters with a molded slot for the laser that also contained a power switch. When holstered, the ECR (Enhanced Combat Readiness) system shuts off the laser via a molded projection. Upon being drawn from the holster, the Reactor 5 is instantly activated and ready for use.
Another smart thing Viridian did was to offer laser/holster pairings. In this case, an outside-the-waistband holster with the ECR system is sold with the Reactor 5 green laser for the Springfield Armory XDS.