I have park assist...actually called EchoMaster...I ordered it and Toyota installed it before I picked my car up. They come in black or color coded. I got black because it was $100 cheaper than color coded, plus they didn't have Jasper Peal anyway. The black was $395, color coded was $495. I've seen them on a lot of Lexus cars here, but of course, theirs are color coded..

There is a little black box mounted on the left hand corner of the rear window, above the back seat. I assumed the sound came from that black box, which has a control for loud or soft. You can hear it inside the car but not outside of the car (unless of course you have it set on loud and roll the rear window down).

I feel safer with these on, especially since people can't hear the car coming when you back up.