A method for monitoring presence in a surveillance area by a surveillance system comprising the following steps: - detection of an absence of motion or at least one motion of at least one entity (E1, E2, En) in a detection area of the surveillance area by a surveillance device of the surveillance system, - creation and/or modification in the memory of the surveillance device of motion information relating to the absence of motion or at least one motion of at least one entity (E1, E2, En) detected during the step of detecting the absence of motion or the at least one motion, - sending of the motion information by the surveillance device to a processing unit of the surveillance system, the processing unit being arranged to emit a query to a listening module of the surveillance system upon receipt of motion information, said query corresponding to a request to obtain presence information, - detection by the listening module of the surveillance system of an absence or presence of at least one terminal (T1, T2, T3, Tn) in a communication network, the listening module being arranged to communicate with a router of the surveillance system and being provided with a packet analyzer configured to detect in at least one data packet exchanged in the communication network and received from the router said absence or presence of at least one terminal (T1, T2, T3, Tn) in the communication network, the communication network being extended in the surveillance area, - creation and/or modification in the memory of the listening module of presence information, the presence information relating to the absence or presence of at least one terminal (T1, T2, T3, Tn) in the surveillance area detected during the step of detecting the absence or presence of at least one terminal (T1, T2, T3, Tn), - sending of the presence information by the listening module to the processing unit, the step of detecting at least one motion of at least one entity (E1, E2, En) is followed by the step of detecting the absence and/or presence of at least one terminal (T1, T2, T3, Tn) in the communication network, the detection step being carried out after an entity has been detected in the step of detecting at least one motion, an intrusion being detected by the surveillance system when there is no correspondence between a motion detection and a terminal (T1, T2, T3, Tn) detection. - detection of an absence of motion or at least one motion of at least one entity (E1, E2, En) in a detection area of the surveillance area by a surveillance device of the surveillance system, - creation and/or modification in the memory of the surveillance device of motion information relating to the absence of motion or at least one motion of at least one entity (E1, E2, En) detected during the step of detecting the absence of motion or the at least one motion, - sending of the motion information by the surveillance device to a processing unit of the surveillance system, the processing unit being arranged to emit a query to a listening module of the surveillance system upon receipt of motion information, said query corresponding to a request to obtain presence information, - detection by the listening module of the surveillance system of an absence or presence of at least one terminal (T1, T2, T3, Tn) in a communication network, the listening module being arranged to communicate with a router of the surveillance system and being provided with a packet analyzer configured to detect in at least one data packet exchanged in the communication network and received from the router said absence or presence of at least one terminal (T1, T2, T3, Tn) in the communication network, the communication network being extended in the surveillance area, - creation and/or modification in the memory of the listening module of presence information, the presence information relating to the absence or presence of at least one terminal (T1, T2, T3, Tn) in the surveillance area detected during the step of detecting the absence or presence of at least one terminal (T1, T2, T3, Tn), - sending of the presence information by the listening module to the processing unit,