Some Hilton properties in London (Kensington and Tower Bridge come to mind) have tried this on me before.

In all the cases I have challenged front desk take and got the fees waived. I did not go in to detail as most front desk staff would not have any idea what constitutes "a device".

For example:
I have two laptops but only use one at a time. Due to business reasons I tend to have a few virtual machines on each laptop. Each virtual machine presents a differnt "hardware ID" even though it is running on a single "device".

So when the front desk queried by some one more technically competent they accept this explanation. Tot he front desk staff I just say " Are you accusing me of having more than one person in the room or saying I cam capable of using multiple computers at the same time?"