Senior people inevitably experience the deterioration of cognitive functions and physical capabilities. Studies showed that elderly people are more likely to be involved in collisions in complex traffic situations. As the number of elder scooter riders is rising around the world, this study presented a hazard warning helmet aimed to help the elderly avoid traffic hazards and possible collisions. Our helmet was designed to provide visual warnings of fast approaching vehicles when elder riders pass through double-parked vehicles. An observational study was conducted to evaluate the effectiveness of the helmet design. Five elderly participants were recruited to wear our helmet and a conventional helmet respectively to interact with 50 double parked vehicles (including cars and scooters). Participants’ behavioral reactions were observed and recorded. Results of the study identified four behavioral reactions to double parked vehicles: (1) reducing speed when passing through (without looking back), (2) reducing speed and looking back before passing through, (3) looking in the side mirror before passing through, (4) passing through without taking precaution. Results also showed that participants wearing our helmet were more likely to reduce speed before passing through double parked vehicles than those wearing a conventional helmet. This work has contributions on (1) lowing traffic collision rates, (2) helping elder scooter users be more aware of traffic hazards, and (3) improving elder scooter users’ risky behavior.