Re: "...can pick up the signal from keys..."
Relay Attack. Clever. Thanks for pointer.
MB will have to update their software so that when the key fob signal fades away, the car explicitly counts down to engine off. Give an owner time to turn around to fetch their forgotten key, but not much more than that. Wouldn't it already do that?
The Top Gear idiots once moved Hammond's car out into the middle of the street. Hammond's car had an RFID system with far too much range, no Relay equipment required to take the car a half block away.
My dealer provides C-class loaners when my '08 is being serviced, and the loaners are often keyless. It's actually slightly less convenient than just using a key. The safety procedures take 3s, vice a key needing 1s. Ever so slightly worse. My older car would be already moving before the new one got started.