Function tail light output 5 lumens dimensions 25 x 25x 70 mm weight 53g get started 1 pop open the light with a coin 2 take out the battery saver tab check your when you slide the battery back in 3 slide the unit back together firmly 4 press and hold the onoff switch for about 1 second to turn light on press the onoff button quickly to scroll between light modes low battery indicator when the battery in the light is getting low a little red light w