Thwart potential theft
 

This article caught my attention this morning.

New York Times columnist falls prey to signal repeater car burglary | Ars Technica

While I do not hang out nor live in high crime areas, prudence is still the better part of valor. This got me thinking, "Where could I place a simple SPST (single pole single throw) toggle switch to thwart a drive-off of my X5?"

The "where" actually being which circuit could I easily cut with a simple switch?

The toggle could be in the foot well, or under the dash and cut a circuit in the fuse panel or inside the engine compartment, two wires running a short distance.

Any ideas on which circuit(s)?

Ciao,
Dick

With how everything is interconnected, you could do more harm than good. If you had to pick something, either the fuel pump relay or the starter.

Buy good theft insurance and quit worrying about it. Don't leave anything valuable in it.

Another reason "comfort access" is a total waste of money.

This feature is found on page 91 of my 2005 E53 owners manual.
I don't know if this option continued thru other models but it may be
useful. Truth be told if someone really wants it they'll find a way to
steal it.

This choice is found in the MID Multi-Information Display.
The MID serves as the central display and operation for the following onboard systems:
>Digital clock, e.g. time display, date
>Audio systems: radio, cassette, CD
>Computer, e.g. fuel consumption, cruising range
>Telephone, e.g. dialing.

Extended immobilizer function
You can establish a code that will prevent
the engine from being started
unless the code is entered

Like this:
TOUCH KEYLESS

Not the way we and other families use it multiple times a day.