SECURITY ALARM DEVICE Russian patent published in 1997 - IPC

FIELD: security devices for protection of home and office premises, cars. SUBSTANCE: device has sensitive element, for example, microphone, low-pass filter, sound frequency amplifier, voltage divider, which has serial circuit of first and second controlled resistors, comparator, integration circuit, Schmidt flip-flop, and negative feedback circuit. Sensitive element is connected through serial circuit of low-pass filter and amplifier to first input of comparator and voltage divider, which is inserted between output of sound frequency amplifier and common line. Output of comparator is connected to serial circuit of integration circuit, Schmidt flip-flop and inverter which output is connected to input of negative feedback circuit. second in of comparator is connected to terminal of second controlled resistor in voltage divider and to output of negative feedback circuit. EFFECT: increased functional capabilities, increased sensitivity, increased selectivity of checking the amplitude of electric signal. 2 dwg