Hi.
I just found what looks like a spare key fob clipped into the back of the glove box on my E60 535d M sport, what is it?

 

A picture is worth a thousand words.

 

its for your plastic valet key to slide into in case you don't have your standard keyfob. That way you can still stick the key into the ignition and start the car.

 

Not sure I have a plastic valet key, not found that yet? Will look in manuals that were with it. Thanks.

 

Probably is your spare key. There is a charging port in your glove box which is supposed to be used to keep your spare key fully charged.

 

can't find any plastic key, it is defo not my spare fob, or where it charges, there is no pwer to the case it sits in.

 

It is definitely a spare key it is referred to as key number 3 as you should have to two fobs that came with your car. It's written in your manual and no it does not charge it is simply a "holster" if you will for the spare key which could also be a valet key.

 

Here is a link to what I think you're referring to. It takes both parts to function. The car has to be optioned with it or they can be purchased afterwards.
BMW 3 Series 2006-2011 E90 BMW Valet Key

Excuse the name of the link, as you can see near the bottom of the page it applies to a number of different series.

 

that's it, just got to find the actual plastic key now!