Ford is developing a seat belt that inflates when the car detects a crash. In The Wall Street Journal, Matthew Dolan writes:
Its inflatable rear seat belts spread crash forces over five times more area of the body than conventional seat belts, said Sue Cischke, Ford group vice president of sustainability, environmental and safety engineering
Each belt's tubular air bag inflates with cold compressed gas, which flows through a specially designed buckle from a cylinder housed below the seat. The inflatable belt's accordion-folded bag breaks through the belt fabric as it fills with gas, expanding sideways across the occupant's body. It looks something like a water wing children wear in the pool before they know how to swim.
Link via Popular Science