The install was completed yesterday afternoon. I am 100% happy with the result, both visually and functionally. To recap, the sensor kit came from Cobra in the UK. They exactly match what the manufacturers use, so they mount flush in the bumper. Since they were painted to match, the only thing this is visible is the small grommet ring around the sensor.
Functionally, the rear sensors are activated when Reverse is selected. They beep at an increasing frequency as you approach an object, with a continuous tone at about 2 feet. The front sensors are active when the ignition is on, but can be turned off with a hidden switch that was conveniently mounted in the center stack. This is useful so that you don't hear any beeping while driving in stop and go traffic. There are separate speakers front and rear that you can distinguish by tone. So everything looks and works exactly as if it was done by the factory, with the exception of any visual cues, which I don't have in any of my other cars with parking sensors.
The work was performed by Sound Innovations in Hayward, CA. These guys do such good work that of 42 reviews on Yelp, 39 are 5-star! If you live in the Bay Area and are potentially interested in having them upgrade your Model S with these sensors, PM me for pricing info.
