The Water Activated Dive Marker Light can flash for up to 500 hours which far exceeds most marker lights on the market. ... This Water Activated Dive Marker Light is a disposable marker light with non replaceable batteries. Great way to keep track of divers, snorkelers or just swimmers .Comes in Red,Blue and Green lights 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.