Smart electricity monitors with unique identities placed at individual power outlets within a building communicate frequent power measurements to a service which determines, from this power usage data, which outlets are associated with occupied seats within the building. This occupancy information can be used to update an occupancy model for the building that is used to forecast the building's occupancy. Based on present occupancy, projected occupancy, and other data, in some instances, the building's thermostats can be controlled and unoccupied seats can be assigned dynamically.