I notice on e-bay you can grab one of these older style 3 button remotes for $20-30 in some cases for a GREAT looking OE key.
may be worth the insurance to own one and strap it to car somehow in a nice hidden waterproof area/case.

EDIT: I bought a small weatherproof case and this e39 key fob and programmed it to my car and hit is somewhere on my vehicle. even if someone found the key, they could steal whats inside, but never drive away with vehicle.

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I swear, my cars are like a girlfriend.
Sometimes its a rough ride, sometimes its smooth motorin'.
Sometimes she doesnt like how i treat her and sometimes i dont like how she behaves.
BUT at the end of the day, she loves it when I am inside her.

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'91 850i
'05 X5 4.4i
'09 Clubman S