The device operates as follows: The flowing medium presses against the paddle for the flow switch. The paddle is fitted to one end of a balance arm which is in direct contact with a prestressed leaf spring. At the other end of the balance arm is a permanent magnet. This magnet actuates a reed contact located within a moveable housing outside the media. The reed contact switches on or off depending on the position of the permanent magnet and the switch housing. The status of the switch may then be used to electrically control the fluid flow. The moveable reed switch on the unit allows the contacts to be set either normally open (N/O) or normally closed (N/C).