Patent ID: 6720875
Filing Date: 2004-04-13
Classification: G08B

Abstract:
An alarm device comprisingan acoustic pressure sensor supplying an analog signal to a first amplifier and to a second amplifier; a first comparator having a positive input connected to an output of said second amplifier and wherein said first comparator's output delivers a warning signal to an alarm when there is a break-in or a break-in attempt; self-adjusting means comprising an analog-digital converter having an input connected to an output of said first amplifier and wherein analog-digital converter's output is a digital signal which varies in accordance with an atmospheric disturbance, and a microprocessor programmed to deliver, in response to the detection of said digital signal supplied by said converter, a digital signal at a negative input of said first comparator, the pulses of which have a variable width which increases in accordance with the duration and the strength of said atmospheric disturbance so as to automatically increase a triggering threshold of said alarm and hence reduce its sensitivity when said acoustic pressure sensor detects an atmospheric disturbance.