A new sensor could let them (or their coaches) know, and it would go on their neck, not their head.
Although a number of groups have developed helmet-integrated sensors that detect the type of impacts associated with concussions, such devices aren't necessarily 100-percent reliable. In some cases, they may sound an alert when no concussion has occurred, or they may dismiss an impact that has caused such an injury.
Seeking a more accurate alternative, Michigan State University's Prof. Nelson Sepúlveda noted that when college football players received head impacts, their head rapidly moved whiplash-style to one side. Working with graduate student Henry Dsouza, he proceeded to develop a thin-film adhesive-patch sensor that could detect the telltale neck movements.
Roughly the size of a small bandage, the prototype device is only about 0.1 mm thick, and it incorporates a piezoelectric material that produces an electrical charge when stretched or compressed. The charge data is relayed to a computer, which analyzes it to determine if a concussion-grade impact has occurred.
In a test of the technology, accelerometers were placed within a dummy head, plus some of the "bandage" sensor patches were applied to the front, back and either side of that head's flexible neck. The head was then dropped approximately 2 ft (0.6 m) onto a hard surface.
When readings from the patches were compared to those from the accelerometers, it was found that the two systems performed equally well at detecting concussion-causing impacts. Unlike helmet-integrated accelerometers, however, the sensor patches wouldn't produce false readings caused by factors such as the helmet sliding relative to the head.