With reference to FIG. 1, a typical room 10 containing a MRI scanner 20 is illustrated. The scanner 20 contains a powerful magnet 30. The magnet 30 emits a magnetic field 40 which is strongest at either opening of a bore 50 and decreases with distance away from the magnet. A subject is placed on a patient conveyance 60 or couch which moves in the bore 50 during scanning Warning lines 70 are often marked on the floor, which provide caregivers reference points regarding the increasing strength of the magnetic field 40, e.g. a 3000 gauss line, a 5000 gauss line, a 10000 gauss line or the like. A device 80 is connected to a power source 90. Some power sources are portable and include a battery. Other power sources include electrical power outlets.