Abstract: A presence-detection-system tag in which a frequency-dividing transponder may be decisively deactivated notwithstanding the intensity of the ambient magnetic field.

Abstract: An intrusion alarm system, for an enclosed space responsive to frequencies in the one to two Hertz range for detecting opening of doors or windows; and responsive to frequencies in the three to four Khz range for detecting breaking glass. A detected frequency in the one to two Hertz range increases the sensitivity required for detecting breaking glass.

Abstract: The pressure measuring device has a housing in which a pressure chamber is located in a pin extending freely in the interior of the housing from a base. The pressure chamber wall is deformable elastically under an applied pressure. In the free end portion of the pin a magnetoresistive sensor is mounted which is moved with the chamber wall in a displacement occurring because of pressure changes in the chamber and thus is displaced relative to a permanent magnet. The magnet is mounted slightly transversely in the end portion of a compensating sleeve which surrounds the pin with wall contact. The change of the magnetic field at the sensor on displacement causes a proportional resistance change of the sensor so that an electrical signal proportional to the pressure change is generated which is a measure of the pressure. An amplifier for the signal from the magnetoresistive sensor can be mounted inside the housing adjacent the permanent magnet or the magnetoresistive sensor.

Abstract: Ice formation on an aircraft surface swept of an air flow is detected by using an electrical heater which produces a small limited amount of heat to, on the one hand a heat flow meter and, on the other hand to a heat sink. When there is no ice on the transducer it produces a large output signal but when ice forms on the transducer the ice, due to its high resistance to heat flow, causes a change in balance between the two heat flows and a change in output of the heat flow measuring transducer.