Abstract: A system detects the level of a liquid contained in a liquid gas tank or the like by using a magnet. This system is mounted on a tank (1). The tank is usually provided with a mechanical level indicator. The mechanical level indicator transmits a certain angular rotation to a stem (2). The upper end of the stem is connected with a magnet. The magnet is placed within a flanged body (3) which is fixed on the tank surface. A casing (4) including a transmitting apparatus (6), coupled with at least a magnetic reader (5) is arranged out of the tank (1) and over the magnet which is placed within the flanged body (3). On the basis of the angular displacement of the magnet, the transmitting apparatus and magnetic reader translate the filling level of the tank in signals to be transmitted to suitable receiving devices.