SODIAL(R) 5 LED Front Bike HeadLight + 9 LED Rear Flashlight + Wireless Bike Speedometer Which wireless Bike built ball switch, sleep when the body shaking table, vibration sensors automatically turn the ball switch; Chronograph with waterproof function can be used in the rain, but not Qinru water use; Code table on the back battery cover is open, being careful not to waterproof gasket lost; Probe and the magnet should be a 2mm sensing range, within the handlebar diameter 2.5CM Stopwatch Specifications: High: 5.1cm Width: 4.6cm Thickness: 2cm