Anykey

Say you would like to go to a secure hotel room. You're some kind of important government official and would prefer to have a room where not any maid/spy can enter. You need to stay at a hotel with the Anykey system.

The Anykey locking system looks like a normal lock from the outside - just a place to insert a key. It also looks nearly the same from the inside - only you insert a key upside down. Here's the catch. You bring the keys with you. Since they are your keys you have no fear of stray manager/spy entering your room. It's not electronic, so nobody can hack in. You insert your master key on the inside, and until removed only your slave key will work.

How about this for inner workings. All you'd have to do is make the inside key with grooves in the opposite direction of the outside key (high lump close in on #1 = high lump far out on key #2). The inside key would be inserted upside down. Pins on the inside key are welded to little tubes each with an inner diameter of a pin. The tubes serve the function of the normal core instead of lining up to make a cylinder.

What about lock pickers? One might ask (hi jutta). Well, picking a lock is not a problem for true experts, but same with kicking your door down. This idea is not meant to completely replace existing security measures, but add a layer that doesn't currently exist - against the owners of the lock.