A method for monitoring a predetermined space, with said predetermined space comprising an authorised zone and an unauthorised zone, characterised in that it comprises the following steps: - a) preparing at least one first volumetric sensor for detecting a first movement signal representative of movement in the authorised zone of said space; - b) preparing at least one second volumetric sensor for detecting a second movement signal representative of movement in the unauthorised zone of said space; - c) processing said first signal and second signal for identifying a movement in said space; - d1) preparing a status variable able to adopt a first value indicative of the presence of at least one person in said space and a second value indicative of the absence of persons in said space; - d2) analysing the first and second signals for detecting a movement inside the authorised zone and the unauthorised zone and evaluating whether the movement detected has been detected in the authorized zone or in the unauthorized zone; d3) following identification of a movement: - e) making available an alarm indication if said status variable has said second value and said movement was initially detected in said unauthorised zone; or - f) if said status variable has said second value and said movement was initially detected in the authorised zone, setting the status variable to the first value and resetting and activating a countdown of time; or - g) if said status variable has said first value, resetting and activating the countdown of time; - h) setting the status variable to said second value if said countdown of time has finished without detecting any further movement. - a) preparing at least one first volumetric sensor for detecting a first movement signal representative of movement in the authorised zone of said space; - b) preparing at least one second volumetric sensor for detecting a second movement signal representative of movement in the unauthorised zone of said space; - c) processing said first signal and second signal for identifying a movement in said space; - d1) preparing a status variable able to adopt a first value indicative of the presence of at least one person in said space and a second value indicative of the absence of persons in said space; - d2) analysing the first and second signals for detecting a movement inside the authorised zone and the unauthorised zone and evaluating whether the movement detected has been detected in the authorized zone or in the unauthorized zone; d3) following identification of a movement: - e) making available an alarm indication if said status variable has said second value and said movement was initially detected in said unauthorised zone; or - f) if said status variable has said second value and said movement was initially detected in the authorised zone, setting the status variable to the first value and resetting and activating a countdown of time; or - g) if said status variable has said first value, resetting and activating the countdown of time; - e) making available an alarm indication if said status variable has said second value and said movement was initially detected in said unauthorised zone; or - f) if said status variable has said second value and said movement was initially detected in the authorised zone, setting the status variable to the first value and resetting and activating a countdown of time; or - g) if said status variable has said first value, resetting and activating the countdown of time; - h) setting the status variable to said second value if said countdown of time has finished without detecting any further movement.