Some sort of magnetic/electronic system used in MRI's.
At my job (hospital), there is a very big door with the words "Magnetom" on it located in the CT Scan area. It has about 20 locks and handles and bolts on it. There are several warnings that say not to wear watches or pacemakers or anything metallic/electronic near it. I can never get close to the door because it scares me...it emits a very loud humming noise...I have no idea what's on the other side of that door!!