Magnetic field
From Tardis Wiki, the free Doctor Who reference
Magnetic field was a form of technology that attracts metals.
The bodies of Magnedons were held together by an internal magnetic field and the First Doctor believed that they could attract other metallic creatures to prey on them. (TV: The Daleks)
A Dalek duplicate of Ralph Hellcombe emitted a magnetic field when the Eleventh Doctor used Ball bearings to learn where the field came from. (COMIC: The Dalek Project)
