When the "Micro Cooling Fan" piece of ferromagnetic metal or other permeable materials with close when the action occurred, opened or closed circuit. By the permanent magnet and reed pipe. Permanent magnet, reed nor fixed with a non-magnetic magnetic bracket. To connect the north and south poles of the permanent magnet as the axis, the axis should coincide with the axis of the reed or substantially coincide. By adjusting the distance far and near permanent magnet and reed switch between the reed just when the action occurs, the position of the magnet fixed. At this time, when there is "Micro Cooling Fan" piece of magnetic material, such as iron is also close to the magnet and reed switch, reed action will happen again, back to the state when there is no magnetic field; when the iron leave when the reed that occur in the opposite direction of motion. "Micro Cooling Fan" reed relays, solid structure, contacts are sealed, high durability, can be used as the location of mechanical equipment limit switch can also be used to detect iron doors, windows, etc. are at the specified location.