The HANS device (also known as a head restraint or Head and Neck Support device) is a safety item compulsory in many car racing sports. It reduces the likelihood of head and/or neck injuries, such as a basilar skull fracture, in the event of a crash.
The HANS Device
Revolutionalizing Safety in Motorsports
The purpose of the device is to stop the head from whipping forward in a crash, without otherwise restricting movement of the neck. In a crash, an unprotected body is decelerated by the seatbelt with the head maintaining velocity until it is decelerated by the neck.
The HANS device maintains the relative position of the head to the body, with the device transferring energy to the much stronger chest, torso, shoulder, seatbelts, and seat as the head is decelerated.