Methods, apparatus and systems for detecting and monitoring vital signs and other periodic motions of an object are disclosed. In one example, a system for monitoring object motion in a venue is disclosed. The system comprises a transmitter, a receiver, and a vital sign estimator. The transmitter is located at a first position in the venue and configured for transmitting a wireless signal through a wireless multipath channel impacted by a pseudo-periodic motion of an object in the venue. The receiver is located at a second position in the venue and configured for: receiving the wireless signal through the wireless multipath channel impacted by the pseudo-periodic motion of the object in the venue, and obtaining at least one time series of channel information (TSCI) of the wireless multipath channel based on the wireless signal. The vital sign estimator is configured for: determining that at least one portion of the at least one TSCI in a current sliding time window is associated with the pseudo-periodic motion of the object in the venue, and computing a current characteristics related to the pseudo-periodic motion of the object in the current sliding time window based on at least one of: the at least one portion of the at least one TSCI in the current sliding time window, at least one portion of the at least one TSCI in a past sliding time window, and a past characteristics related to the pseudo-periodic motion of the object in the past sliding time window.