| 摘要 |
A pressure sensor or microphone 19 is used in combination with an electronic circuit in order to detect the movement of a person or intruder within or into an enclosed space which may be a vehicle or building. Changes in air pressure caused by the movement of said person across flexible floors or by the movement of doors is changed into an electrical signal by the pressure sensor. The electronic circuit includes a frequency filter 21 which separate the required signal from other frequencies which may be present. The filtered signal is compared to a reference voltage at 23 such that when a signal of sufficient amplitude and in the chosen frequency range is detected an alarm or other electrical system is activated. The reference voltage is continually adjusted to match the background noise level. <IMAGE> |
