All these people are wearing a helmet but you would never notice it if I didn't tell you about it. The airbag is shaped like a hood that surrounds your head. The gas inflater that inflates the airbag is placed in a holder in the collar on the bicyclist's back. The airbag is deployed by sensors – accelerometers and gyros – that pick up a bicyclist's abnormal movements in the event of an accident.
Source: hovding
Source: hovding