A circuit (10, 11) comprising: a magnetically sensitive latching device operatively configured and arranged to change from a first output state to a second output state as a function of a magnetic field applied in a first direction, to maintain said second output state when said magnetic field is no longer applied in said first direction, and to change from said second output state to said first output state as a function of a magnetic field applied in a second direction; a power switching device coupled between a power source and a load; said power switching device coupled to said latching device and said latching device and said power switching device operatively configured and arranged such that said power switching device connects said power source and said load when said latching device is in said second state and disconnects said power source and said load when said latching device is in said first state; said latching device coupled to said power source between said power source and said power switching device; a magnetic switching device having an open disconnected default state and operatively configured and arranged to change from said open default state to a closed connected state when said magnetic field is applied in said first or second direction and to return to said open default state when said magnetic field is removed; characterised in that said magnetic switching device is between said latching device and said power source; and in that said latching device and said magnetic switching device spatially aligned such that said magnetic field applied in said first direction causes said magnetic switching device to change from said open default state to said closed connected state, thereby powering said latching device, and said latching device to change from said first state to said second state, thereby signalling said power switching device to connect said power source and said load. a magnetically sensitive latching device operatively configured and arranged to change from a first output state to a second output state as a function of a magnetic field applied in a first direction, to maintain said second output state when said magnetic field is no longer applied in said first direction, and to change from said second output state to said first output state as a function of a magnetic field applied in a second direction; a power switching device coupled between a power source and a load; said power switching device coupled to said latching device and said latching device and said power switching device operatively configured and arranged such that said power switching device connects said power source and said load when said latching device is in said second state and disconnects said power source and said load when said latching device is in said first state; said latching device coupled to said power source between said power source and said power switching device; a magnetic switching device having an open disconnected default state and operatively configured and arranged to change from said open default state to a closed connected state when said magnetic field is applied in said first or second direction and to return to said open default state when said magnetic field is removed; characterised in that said magnetic switching device is between said latching device and said power source; and in that said latching device and said magnetic switching device spatially aligned such that said magnetic field applied in said first direction causes said magnetic switching device to change from said open default state to said closed connected state, thereby powering said latching device, and said latching device to change from said first state to said second state, thereby signalling said power switching device to connect said power source and said load.