SteriPEN is the world's leading manufacturer of ultraviolet, handheld water purifiers. SteriPEN water purifiers quickly and easily make safe drinking water available for travel, outdoor recreation, and emergency situations at a fraction of the cost of bottled water. SteriPEN Adventurer Opti's ultraviolet (UV) lamp destroys over 99.9 percent of harmful microorganisms in water. UV purification works as the cells of microbes absorb ultraviolet energy emitted by the lamp so they can't reproduce to make you sick. Great for camping, hiking and backpacking. Adventurer Opti has easy-to-use 1 button operation. LED light quickly indicates when ready to purify. Place the lamp in clear water and stir until indicator light turns green. Purify a half-liter in 48 seconds or a liter in 90 seconds. Automatic shut off when treatment is complete. Unclear water should be pre-filtered prior to treatment. Device includes a revolutionary, patented optical eye safety feature to sense water so the UV light only turns on when safely below water surface. The UV lamp provides up to 8,000 one-liter treatments. One set of batteries purifies 50 liters. Works in containers with minimum 1.75 inch diameter opening (i.e. Nalgene wide-mouth bottles). Low power indicator lets you know when batteries need replacing. Includes black neoprene case with belt loop and 2 CR123 batteries, instructions and 3-year limited warranty.