A method of detecting and quantifying human objects in a given environment by passively observing wireless signals in an interesting environment. Information pertaining to observed wireless signals, such as wireless physical layer data and metadata, encrypted or unencrypted data and metadata in the wireless media-access control layer, and channel state information are extracted from the observed wireless signals and used to detect and quantify human objects in a location. The signals that are observed can originate from a wireless object used by a target of interest, such as cellular phone or workstations, or from infrastructure devices, such as wireless access points, IoT devices, or other transceivers. The signals can also originate from other recognizable signal sources, such as electromagnetic interference introduced by equipment such as elevator motors or microwave ovens.