An MRI protector for protecting personnel and the MRI apparatus from the introduction of ferrous articles into the magnetic field of the MRI has an array of Hall effect sensors oriented to scan the magnetic field of the MRI. The Hall effect sensors are oriented to scan the magnetic field at the access door of the shielded MRI room. The sensors are connected to a central processing unit (CPU) which analyses the output of the sensors and propagates a warning when the presence of ferrous articles affects the magnetic field of the MRI.