Abstract: An athlete measures sprint time by locating a smartphone having a camera and clock start button which is first activated at the finish line. The sprint end time is recorded by a photo stamp time app. This sprint end time activates a video trigger causing the smartphone to send a RF stop event signal to a wrist mounted motion sensor worn by the athlete. A sensor timer is started via the start event by track or self starting. In track starting, the athlete pushes a start button on the sensor to initiate a variable 2-5 second delayed sound READY-SET-GO series of beeps to start the sprint. In self starting, the sensor detects threshold motion parameters of the sprinter's start which activates the sensor's free running clock and saves the start time. The time base on the sensor is used to calculate run time.