Abstract: The operability of one or more audio speakers is monitored by continuously transmitting a non-audio signal on the lines connecting to the speakers and providing a vibration sensitive transducer such as a piezoelectric transducer which continuously picks up the signal. The output from the transducer couples to detection circuitry which may comprise an amplifier and gate or trigger circuit. The output of the detection circuitry couples either via the existing speaker lines or via a separate supervision line to an alarm device. When the speaker or speaker lines are inoperative the non-audio signal is not present and the gate circuit transmits an alarm signal to an alarm device. In one embodiment the detection circuitry is supplied power directly from the speaker lines via a rectifier means. In another embodiment the detection circuitry includes an oscillator, one associated with each speaker and each constructed to oscillate at a different frequency.

Abstract: An ionization detecting fire alarm device that comprises a double chamber structure, a source disposed in at least one of the chambers and a vernier adjusting screw electrode protruding into one chamber. The chamber containing the adjustable electrode is more open to the atmosphere than the other chamber, porting is provided between chambers and detection occurs by sensing the rate of change of ionization current in the chamber structure. The source or sources, one being in each chamber, is a beta source such as a nickel 63 source. A change in ionization current is detected by a unique circuit of this invention which comprises a programmable unijunction transistor oscillator circuit.

Abstract: The detector comprises a chamber having at least one radiation source disposed therein. The chamber includes spaced collector plates which form a part of a detection circuit for sensing changes in the ionization current in the chamber. The radiation source in one embodiment is in the form of a wound wire or ribbon suitably supported in the chamber and preferably a source of beta particles. The chamber may also include an adjustable electrode and the source may function as an adjustable current source by forming the wire or ribbon in an eliptical shape and rotating the structure. In another embodiment the source has a random shape and is homogeneously disposed in the chamber.