A method to synergistically sense occupancy inside a building. A coarse-grained sensor in the building generates a coarse data indicating a user is in a large area including a control zone. A fine-grained sensor in the building generates a fine data indicating the user is in a small area. The fine data is more accurate but less reliable than the coarse data. The method to improve energy efficiency by generating an actuation plan for the control zone. The method includes receiving the coarse data and the fine data, normalizing the coarse data and the fine data, checking for an overlap between the large area and the small area, calculating a change in occupancy in the control zone based on the normalized coarse data if there is no overlap and based on the normalized fine data if there is overlap, and generating the actuation plan based on the change in occupancy.