The Lazer Eye Nock from Carbon Express fits directly on the end of your arrow and illuminates to allow you to follow the flight of your arrow and determine the location of impact on your target. Knowing the impact location prevents arrow loss and aids in recovery. Lazer Eye Nock activates upon release of the arrow, when the bow string compresses forward and presses the nock onto the arrow. Illuminates on each and every shot. Turns off by slightly pulling the nock approximately 1/16" off of the shaft. Durable construction for repeated use. Equates to no difference in arrow flight or impact area up to approximately 40 yards. Offers up to 7 hours of illumination. Pack of 2.