In an indoor environment on fire, automatic deployment of sensors disposed on, beneath or over the floor to look upward the ceiling to observe a body of smoke and flame risen near the ceiling allows important information regarding states and dynamics of the body of smoke and flame to be gathered at an early stage of fire (e.g. before arrival of firefighters). By distributing the sensors over the indoor environment, the states and dynamics of the body of smoke and flame are monitored holistically (i.e. as a whole) even at the early stage of fire. Such information is useful to predict development of the fire. In one implementation, a sensor is held in an infrastructure sensor holder mounted on the ceiling during normal time. Upon detecting occurrence of fire, the sensor drops from the holder to land on the floor and orients a sensing direction vertically upward to perform monitoring.