Measuring head impacts in helmeted sports is important for prognosticating onset of mild traumatic brain injuries (MTBIs) or concussions. In this paper we present a miniature battery-less, self-powered sensor that can be embedded inside sport helmets and can continuously monitor and log the statistics of different levels of helmet impacts. At the core of the proposed sensor is a novel time-dilation circuit which allows measurement of the high-levels of impact energy. An array of linear floatinggate injector is used for storing the location of the sensor on the helmet and for logging the statistics of helmet impacts which can be retrieved using an external plug-and-play reader. Measured results from prototypes fabricated in a 0.5 μm CMOS process validate the functionality of the sensor when subjected to controlled drop tests.