Abstract: A mercury switch assembly is adapted to be secured to an anterior horizontal surface of a patient and connected to an electrical alarm system. The switch assembly comprises a head chamber and a foot chamber connected by a throat passageway. A ball of mercury moves from the head chamber through the throat passageway and into the foot chamber to complete an electrical circuit when the switch assembly is tilted from horizontal by a predetermined degree of inclination. The head chamber is generally elliptical with lateral extensions. The throat passageway is narrow and shallow. The foot chamber is deep and rounded. The ball of mercury normally lies within the head chamber in the horizontal position, but establishes electrical connection between a novel form of terminals contained in the foot chamber when the tilt threshold of the switch assembly is reached.

Abstract: A mercury switch assembly adapted to be secured to an anterior horizontal surface of a patient and connected to an electrical alarm system. The assembly includes a pair of connected and enclosed chambers which contain a quantity of mercury which moves into contact with electric terminals that project into one of the chambers only when the switch assembly is displaced from horizontal by a predetermined degree of inclination. The assembly contains an elliptical shaped head chamber with lateral extensions connected to a deep rounded foot chamber by a narrow throat passageway. The mercury normally lies within the head chamber in the horizontal position, but establishes electrical connection between the terminals contained in the foot chamber when the tilt threshold of the assembly is reached. The foot chamber retains the mercury in contact with the terminals despite subsequent displacements of the assembly until the device is removed and inverted, thereby causing the mercury to return to the head chamber.