Why don't you go all the way and get the Mercedes key switch with rf fob. This way all you need to do is have the fob in the room and the computer would start with a button and if the fob is removed it won't, should only cost a couple of grand through the MB dealer if I understand their parts mark up !
Hi there
these type of keys are a real nuisance -- battery fails or receiver in the car fails and you are 100% hosed up. Even your average decent Mercedes dealer can't fix these and short of breaking a window and climbing in that way there is NO way to force the door open.
The new ones can even detect whether you are "DUI" and wont let you start the engine. However if YOU are OK but a colleague with you has had "One too many" the detector still wont let the engine start - it doesn't know WHO is the driver - it just detects the Alcohol.
Think a case of "Too Much technology".
Back to the point however -
Some computers can be fitted with Thumb or finger print detectors for example secure machines for CIA personnel etc etc.
Smart card operation has also been around for "Donkeys Years".
Cheers
jimbo