Although it's a long time since I posted on this thread this is relevant to the Mercness.
Leaving the hotel I visited when I went to the Lotherton Hall do I put on a clean pair of trousers and put the ones I had worn in my suitcase. When I went to the car with my suitcase I walked up to it and opened the boot and the suitcase in the boot and shut it as usual. When I tried to open the car door it wouldn't unlock. Oh dear, I thought, or something like that. Then I twigged what it was. The plip was in my other trousers, in the suitcase, in the boot. Rescued the key and all was OK.
The keyless go system recognised the plip let me open the boot but the system is zoned. If the plip is in the outside boot zone it will let you open the boot but not the doors. To open or lock the doors the plip has to be in the outside door zone. You can't lock the doors if the plip is inside the car (not in the outside door zone) so you can't lock yourself out with the plip on the inside.
These Merc safety interlocks are carried over to the West Coast.