Abstract: A fire detector having a first sensor for emitting a first output signal in response to a fire phenomenon, a second sensor for detecting a source of false alarm conditions generated by man and/or machinery and an evaluating circuit. The evaluating circuit has a mechanism for activating an alarm signal when the value of the output of the first sensor exceeds a threshold value. The threshold value is set by the second sensor in response to the detection of signals generated during normal use of the premises to be protected.

Abstract: In a photoelectric smoke detector, a radiation source is driven intermittently by a control circuit and the radiation influenced by smoke particles, for instance scattered radiation, is picked up by a radiation receiver. The signal of the radiation receiver is transmitted to a signal processing circuit which is transmitted to a signal processing circuit which is simultaneously regulated by the control circuit. The signal processing circuit comprises a phase sensitive circuit which reverses or inverts the received signal according to the phase of the signal of the control circuit and transmits the thus modified signal to an integrating circuit. The integrating circuit controls a display circuit by means of its integrated output signal. The display circuit can, for instance, output an alarm signal when the integrated signal, i.e. the smoke intensity, exceeds a prescribed threshold value or can display the smoke intensity.

Abstract: In a scattered radiation smoke detector (D) the energy supply from the evaluation unit (A) and the signal returned thereto take place exclusively optically by means of radiation conducting elements (L.sub.1, L.sub.2) and all electrical components are situated in the evaluation unit (A) remote from the smoke detector (D). An approximately parallel transmitting or reception zone of small diameter is generated by collimating devices (4, 6) disposed at the ends (3, 8) of the optical conductors and thereby the interference radiation level in the smoke detector is reduced and the sensitivity increased. Since the smoke detector (D) comprises no metallic components, it is insensitive to temperature and corrosion and is especially well suited for application in environments subject to the danger of explosion and electrical interference.

Abstract: In an alarm system a central signal station periodically transmits interrogation signals, preferably in the form of infrared radiation packets to remotely located detectors which transmit a response signal back to the central signal station after differing time delays that are characteristic for the individual detectors and which permit the localization of the source of the response signal. In an alarm state, the detectors respond to every interrogation signal, in the normal operational state to only every m.sup.th interrogation signal, i.e. less often, and in a state of diminishing battery potential to only every small p.sup.th interrogation signal, i.e. even less often. The state of the individual detectors is determined from the frequency with which the response signals are transmitted back by the detectors, that is the ratio of the response signals to the interrogation signals.

Abstract: An aerosol detector, for instance a transmission measurement path in a measurement chamber, is provided for the detection of a foreign component in a gas, for instance of incendiary aerosols or smoke in air, and communicates with a reference chamber containing aerosol-free reference gas. The gas in the measurement chamber is periodically exchanged for uncontaminated gas from the reference chamber by a periodical volume alteration of the reference chamber so that, in the presence of aerosols, the aerosol concentration in the measurement chamber and the output signal of the aerosol detector are modulated. The modulation, i.e. the variable portion of the output signal, is an indication of the aerosol concentration or the smoke density. A particularly suitable application is smoke detection in air for the purpose of fire or incendiary reporting or for monitoring air pollution.