To my knowledge you can't install a remote starter on the X5. If you could you would need another coded remote/key to use as a "sacrificial" key remote that would need to be placed in the car permanently. I had looked into a remote starter when I got my 07 and there was nothing on the market.

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2013 BMW X6M-current
2013 Audi S4-current
2007 BMW X5 4.8i (E70)-sold