Method for indicating, assessing and optimising energy consumption for the heating and/or the air conditioning in a dwelling or a like residential building, said dwelling or the like being provided, preferably in each habitable room, with a heating and/or air conditioning means, temperature sensors and presence and/or movement detectors and comprising means for retrieving and transmitting, preferably in a repetitive manner at regular intervals, data delivered by the aforementioned sensors and detectors, as well as by the control units of the heating and/or air conditioning means, said method comprising measuring the air temperature, at least for certain rooms, by means of sensors, subsequently integrating the data collected from the sensors, detectors and units over at least one observation period of several days, preferably of several weeks, and using said data in a remote processing system, particularly by completing a characterisation of the usage habits of the heating and/or the air conditioning and/or at least one correlative analysis of the various types of simultaneously collected data, said method comprising processing the collected data at the remote system that uses said data, so as to determine the average usage level of the heating and/or the air conditioning in a given habitable room according to the level of occupancy thereof or of the dwelling or the like, stated in days present and days absent, for example, and said method comprising providing the user or the occupant with the results of the processing, possibly associated with a quantitative and performance-related assessment of energy use, a recommendation for modifying heating or air conditioning habits and/or proposals for optimising energy consumption for the relevant dwelling or the like, or for at least certain habitable rooms thereof, preferably taking into account comfort criteria for the occupants, said method is characterised in that it comprises measuring the air temperature in the one or more room(s) by means of sensors that are integrated into presence and/or movement detectors of an alarm or surveillance system, and retrieving and transmitting, at regular intervals, the temperature and presence and/or movement data provided by the sensors, the detectors and/or the units towards the remote system that uses the collected data through an alarm unit, surveillance unit or the like that forms a gateway and is linked, on the one hand, to the aforementioned detectors, sensors and units and, on the other hand, to preferably secure, remote transfer means, and in that it comprises establishing, through processing at the remote system, at least two differentiated profiles (P p, P a) of the evolution of the temperature over a base or reference period, typically 24 hours, on the basis of the average hourly temperatures T i p T i a, per room and for all of the rooms equipped with detectors and/or sensors connected to the dwelling or the like, that are computed on the basis of the data collected and assigned to one of the two profiles (P p, P a) as long as the duration of occupancy of the relevant room or of the dwelling or the like, in its entirety, is less than or higher than one or more threshold value(s), with a view to the aforementioned determination of the average usage level per habitable room according to the level of occupancy, in that it further comprises carrying out, at the processing system and on the basis of the average hourly temperatures T i p T i a, an analysis of the heating and/or air conditioning habits for each equipped room, by computing the values of the following two parameters: D i = ∑ i = 1 24 T i p − T i a and D e = ∑ i = 1 24 T i p − T i a 2, with D i = average distance, D e = Euclidian distance, i = number of the time slot, T i p = average hourly temperature for the i th time slot during the days present throughout the observation period and T i a = average hourly temperature for the i th time slot during the days absent throughout the observation period, and in that it comprises issuing a recommendation for modifying heating habits when the value of one of the two parameters (D i and D e) at least is less than a respectively corresponding predetermined threshold (S i, S e), for example S i = 8 and S e = 3.5.