Innovative 500 Hour Water Activated Flashing Marker Light - Red Lights turn on when they come in contact with water and turn off when they are dry. Flashing mode only. Ideal for dawn, dusk and night dives - make divers easy to spot under water and are reusable unlike glow sticks Helps you keep track of your buddy under water Batteries are non-replaceable. Light lasts 500 hours under water.