Self-adjusting alarm device with low energy consumption

An alarm device featuring an acoustic pressure sensor (10) supplying an analog signal to a first amplifying means (12) on the one hand and to a second amplifying means (14) on the other hand, a first comparator (34) whereof the +input is connected to the output of said second amplifying means and whereof the output delivers a warning signal to alarm means (26 and 28) when there is a break-in or a break-in attempt;

• said device being characterized in that it includes self-adjusting means consisting mainly of an analog-digital converter (24), the input of which is connected to the output of said first amplifying means to supply at the output a digital signal which varies in accordance with said atmospheric disturbance and a microprocessor (26) programmed to deliver, in response to the detection of said digital signal supplied by said converter, a digital signal at the −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 the alarm device's triggering threshold and hence reduce its sensitivity when said acoustic sensor detects an atmospheric disturbance such as wind.