A facility for monitoring a predetermined delineated monitoring area, comprising: - at least one acoustic sensor (16, 18, 20, 22, 26, 30) arranged in the monitoring area and designed to convert an acoustic wave picked up following the occurrence of an activity in the monitoring area into an information signal, - a processing device designed for receiving the information signal, - a system for transmitting the information signal to the processing device, - a system for transmitting at least one alarm, and - a database comprising, for each of at least one predetermined reference activity whose occurrence is likely to generate acoustic waves in the monitoring area, reference characteristics relating to said predetermined reference activity, and the processing device including an analysis system designed to: - analyze the information signal according to the reference characteristics of at least one predetermined reference activity of the database, and - activate the system for transmitting at least one alarm according to the analysis of the information signal. characterized in that it comprises, in the monitoring area, at least one acoustic sensor (16, 18, 20, 22) detecting seismic waves propagating in a solid medium, and in that: - the system for transmitting at least one alarm includes a device, arranged in the monitoring area, for generating a level one alarm (44, 46) and a device for generating, to outside of the monitoring area, a level two alarm (56, 60), and - the analysis system is designed to receive an acknowledgment signal and to: • activate the device for generating the level two alarm (56, 60) if no acknowledgment signal is received in a predetermined time period following the generation of the level one alarm, and • update the reference characteristics of a predetermined reference activity in the database if an acknowledgment signal is received in said predetermined time period following the generation of the level one alarm. - at least one acoustic sensor (16, 18, 20, 22, 26, 30) arranged in the monitoring area and designed to convert an acoustic wave picked up following the occurrence of an activity in the monitoring area into an information signal, - a processing device designed for receiving the information signal, - a system for transmitting the information signal to the processing device, - a system for transmitting at least one alarm, and - a database comprising, for each of at least one predetermined reference activity whose occurrence is likely to generate acoustic waves in the monitoring area, reference characteristics relating to said predetermined reference activity, - analyze the information signal according to the reference characteristics of at least one predetermined reference activity of the database, and - activate the system for transmitting at least one alarm according to the analysis of the information signal. - the system for transmitting at least one alarm includes a device, arranged in the monitoring area, for generating a level one alarm (44, 46) and a device for generating, to outside of the monitoring area, a level two alarm (56, 60), and - the analysis system is designed to receive an acknowledgment signal and to: • activate the device for generating the level two alarm (56, 60) if no acknowledgment signal is received in a predetermined time period following the generation of the level one alarm, and • update the reference characteristics of a predetermined reference activity in the database if an acknowledgment signal is received in said predetermined time period following the generation of the level one alarm. • activate the device for generating the level two alarm (56, 60) if no acknowledgment signal is received in a predetermined time period following the generation of the level one alarm, and • update the reference characteristics of a predetermined reference activity in the database if an acknowledgment signal is received in said predetermined time period following the generation of the level one alarm.