Techniques for monitoring presence of a remote device at Layer 2 that allow reducing power consumption without compromising the device’s availability. In its entirety, aside from the required sight sensors situated in an intentionally elevatable sensor housing, the combination sight entails a weapon that is controlled by the sensors. The mobile mining machine may further comprise a tilt device to tilt the cantilever unit and a rotary mechanism to rotate the support arm part and the tool drum. A first comparator circuit has first and second input terminals and a second output terminal. The annular passage may be rendered tortuous by providing the rotor with annular fins which in use project into annular recesses in the stator, and vice versa.