Binary motion events are detected by individual motion sensors placed in a physical environment. The motions events are transmitted to a cluster leader, each motion detector being a cluster leader of immediately spatially adjacent motion sensors. Movements of objects are detected by the cluster leaders according to the motion events. The movements are transmitted to supercluster leaders, each motion detector being a supercluster leader of immediately spatially adjacent motion clusters of sensors. Activities of the objects are detected by the supercluster leaders, and actions of the objects are detected according to the activities.