Not sure that measuring external force is a foolproof indicator of traumatic brain injury, but this could be a great quick-and-dirty way to screen.

I did not realize there's currently no easy way to tell if someone just sustained a brain injury.

There is no easy way to tell if someone has just sustained a brain injury, so soldiers and athletes may unknowingly continue to do the very activity that caused the damage and potentially cause more harm. But a force-responsive, color-changing patch could prevent additional injury, says Shu Yang, Ph.D. "If the force was large enough, and you could easily tell that, then you could immediately seek medical attention," she explains.