I think the handshake with the keyfob is only done in the beginning (for starting). It then monitors that the unit is still inside the vehicle. If the keyfob crosses the boundary (set up by four antennas) it then shows the signal of loss of communication with key. They could easily make a time out counter to shut engine after a certain period and if you want to override your press start or somthing.

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SOLD - 08 X5 (Titanium Silver w/Black Nevada with all options).