Two Modes of Operation :This Helmet Signal Light Has Constant Light Mode and Flashing Mode. Bulit-in Battery : Built-in CR2030 Battery, Constant Working for About 100 Hours. Water Resistance: This Tactical Helmet Flashlight Made Of High Quality Silicone and Nylon Strap. Waterproof. It Can Work In An Environment Of -20 ° C to 50 ° C. Velcro Back Design: With Hook Back, You Can Attach This Safety Flashing Survival Light to Your Helmet, Tactical Vest ,Backpack,Bike Seat and etc. Perfect for Hunting, Cycling, Hiking ,CS, and other Outdoor Sports for Survival Signal and Teammate Identification. Size : 11cmx2.6cm / 4.3inx1.3in . Protable, Lightweight, Easy to Carry and Use.