Do you have Comfort Access? I got notification of a class action lawsuit concerning CA and locking the keys inside the vehicle. Obviously, that shouldn't happen but apparently it can and does. Other then that system - it's mal-operation notwithstanding - there's nothing preventing you from locking the keys in the vehicle unless they're in the ignition slot. That is, a non-CA vehicle doesn't know where the keys are.

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8/2011 X5 xDrive35d Sport, Black Sapphire Metallic, Black Nevada Leather, Fine Burr Walnut Trim
2/2001 M5, Jet Black, Exclusive Complete Black Walk Nappa Point Heritage Leather, Black Cubic Trim