The all new 509® anti-fog fan, stops fog dead in its tracks. If you sweat a lot or just want an extra level of fog stopping protection, the anti-fog fan is for you. This is a removable fan module that installs directly into your existing pair of 509 goggles. Specifically engineered to work with both 509 Sinister & Aviator goggles. In addition, it’s compatible with virtually every other goggle brand on the market. The fan module has 3 settings: Off, On, and Auto. Auto setting automatically detects fog and turns on the fan only when needed. Powered by one AAA battery (included).