A switchable magnetic device of the kind including a housing (12,13), a first permanent magnet, a second permanent magnet, the first and second permanent magnets being mounted within the housing (12,13) such that the first and second permanent magnets (10;11) are rotatable relative to each other, and actuation means adapted to cause relative rotation of the first and second permanent magnets (10;11) wherein the first and second magnets are rotatable relative to each other between a "fully off" position in which north and south poles of the first permanent magnet are in alignment with south and north poles, respectively, of the second permanent magnet and the magnetic device presents a minimal external magnetic field, and a "fully on" position in which the north and south poles of the first permanent magnet are positioned in alignment with the north and south poles, respectively, of the second permanent magnet and the magnetic device presents a maximal external magnetic field, characterised in that the magnetic device is placeable into contact with or in close proximity to an external ferromagnetic material (1050, 1230, 1305, 1420, 1730) releasably attachable to the magnetic device, the magnetic device further includes either one or both of (a) automatic turn-on means (21,30) arranged for automatically switching the magnetic device to an "on" position, in which the magnetic device presents a relatively strong external magnetic field, when the magnetic device is brought into contact with or is in close proximity to the external ferromagnetic material, and (b) automatic turn-off means arranged for automatically switching the magnetic device to an "off" position, in which the magnetic device presents a relatively weak external magnetic field, when the magnetic device is removed from contact with or from close proximity to the external ferromagnetic material, in that the automatic turn-on means (21, 30) include biasing means operatively associated with the first and second permanent magnets (10;11) to bias the relative rotational position of the first and second permanent magnets (10;11) away from the "fully off" position and cause the relative rotation of the first and second permanent magnets towards the 'fully on' position when the device is placed on or in close proximity to the external ferromagnetic material, and in that the automatic turn-off means include rotation limiting means operatively associated with a rotatable one of the first and second permanent magnets (10;11) to releasably hold the rotatable permanent magnet in a rotational position in which the magnetic device presents a strong external magnetic field and which is close to but rotationally off-set from the "fully on" position. (a) automatic turn-on means (21,30) arranged for automatically switching the magnetic device to an "on" position, in which the magnetic device presents a relatively strong external magnetic field, when the magnetic device is brought into contact with or is in close proximity to the external ferromagnetic material, and (b) automatic turn-off means arranged for automatically switching the magnetic device to an "off" position, in which the magnetic device presents a relatively weak external magnetic field, when the magnetic device is removed from contact with or from close proximity to the external ferromagnetic material,