Of note:

There is a notice with my owners manual (2012 X5, Comfort Access,) that the transmitter CAN be accidentally locked in the car. And without a spare key/fob, you are essentially SOL. "Never leave the fob in the car."

Second key and fob are well worth the dealer price. :-)

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Current
2015 BMW F800 GT, Montego Blue
2012 BMW X5 Premium, Vermillion Red
2008 BMW 535xiT, M-Technik body kit, Monaco Blue
2004 BMW 525i Premium, Olive Green.

Past
1991 BMW 750iL, Alpine White.