Toyota Prius needs factory installed reversing beepers

I had disadvantage of parking next to a Toyota Prius, i got out of my car and wondered if the electric motor would reverse the car. I found out. the car made no noise but was inching towards me. My immediate thought was if i was a smaller child i would have no external warning of the car reversing, it had no revving combustion engine. I think hybrid - electric cars should be mandatory factory installed with reversing beepers