20140169135 | METHOD OF DETECTION OF LOW-FREQUENCY AND ULTRASONIC ACOUSTIC SIGNALS WITHIN A PREDETERMINED TIME FRAME - A method for detecting an intrusion in a confined space is provided. The method includes the steps of detecting an ultrasonic acoustic signal with a Doppler shift and a low frequency acoustic signal, said signals being indicative of an intrusion, and generating an alarm if the ultrasonic acoustic signal with a Doppler shift and the low frequency acoustic signal were detected within an assigned timeframe. | 06-19-2014 |