For those worrying about the smart key letting people into your Prius while your walking towards it, you don't have to worry.
The key only allows the door to be opened when it's within approximately 4 foot. My personal experience has even been less, but that's probably because it was in my left pocket and I was using my right hand to open the door. Also, the beeping when the car is on and you get out is by far not a low-volume beep. If you can't hear that, you should probably think about reconditioning either your environment to less than 100 Db or get your hearing checked. It's very audible.