Polarized relays differ from ordinary (non polarized) relays in that they contain a permanent magnet that magnetically polarizes the mobile armature by contact.
While in non-polarized relays the force to which the armature is subjected is proportional to the square of the current circulating through the electromagnet, in polarized relays it is proportional to the intensity of the current. Therefore, while in non-polarized relays the armature is always attracted and always moves in the same direction independently of the direction of the exciting current, in polarized relays the armature moves one way when the exciting current circulates in one direction and in the other way when it travels in the other.