Abstract: An intrusion and alarm sending arrangement having at least one motion sensing device and a first motion signal threshold device has an input connected to said motion sensing device for generating a motion alarm indication in response to a motion signal exceeding a motion threshold determined by said first motion threshold device. At least one infrasonic sensing device is connected to a first infrasonic threshold device having an input connected to said infrasonic sensing device for generating an infrasonic alarm indication in response to an infrasonic signal exceeding an infrasonic threshold determined by said first infrasonic threshold device. A decision device has a motion alarm input and an infrasonic alarm input for respectively receiving said motion alarm indication and said infrasonic alarm indication, and an output, for generating a valid alarm indication upon determining simultaneity of said motion alarm indication and said infrasonic alarm indication.