When you reach your destination and power down the car, the mode icon on the top left of the phone switches from a car to a walking person. As you step away from the car, the watch receives a full download of your car's precise location, the trip distance, the amount of fuel left in the tank, and — apparently for use in case your car is stolen — the car's model name and VIN number.
On some models, though not my loaner CLA, you also get a reading of air pressure for all four tires. I liked these functions, but saw them more as a curiosity than essential aids.
In addition to Mercedes's Pebble integration, I also got a five-minute run-through of how Google Glass could become part of the driving experience. The same diagnostics delivered to the watch after a drive — as well as walking directions from where you parked to where you need to go — can be deployed to Glass. This was my very first experience with Google Glass, so most of my time was spent simply fitting the device to my face and making the screen visible. The simplicity of the watch made more sense for getting a quick read on fuel and tire pressure.
Google Glass is also put to use prior to getting into the car. As you stroll to your car, speak your desired point of interest to Glass. The eyeglass screen then provides walking turn-by-turn directions first to your car, and then driving turn-by-turn instructions to the dashboard navigation. Theoretically, there's no downtime, and the act of driving and living become a single blurred experience.
That idea, and more generally the use of wearables behind the wheel, has some merit. I’m sure that Mercedes and other automakers will continue to experiment. But I have to admit that after a week, I was relieved to return the CLA and Pebble — and get back to my own dumb car, with its simple singular interface designed simply for driving.