| 摘要 |
An infrasonic intruder alarm system 100 comprises a transducer 13 for sensing infrasonic frequency variations, a signal amplifier, an analogue to digital converter which converts a portion of the analogue signal which crosses at least one predetermined threshold into a digital signature, and a processor 15 which compares the digital signature against known digital signatures. An alarm event is triggered if the digital signal produced matches a known signature. Preferably the alarm system detects crossings of multiple positive and negative thresholds. The sequence of threshold crossings and the direction of each crossing is used to determine whether and alarm event will occur. The analogue signal from the transducer (e.g. microphone) may be filtered to remove unwanted frequencies. The alarm system may include a device which monitors a person's health (e.g. heart rate). The processor may include an adaptive self learning protocol. The alarm may be audible, or the system may be coupled to a telephone or ASDL line. False alarms, due to wind for example, are reduced. |
