Abstract: A method for monitoring a site includes calculating a learned threshold time based on a statistical analysis of lengths of time between sensor firings of one or more sensors. A first sensor firing is detected from the one or more sensors. The length of time that has elapsed since the first sensor firing is measured. The length of time that has elapsed since the first sensor firing is compared with the learned threshold time. An alarm condition is generated when the length of time that has elapsed since the first sensor firing exceeds the learned threshold time and no second sensor firing has been detected since the first sensor firing.