The invention concerns an apparatus, system, wearable apparatus and concomitant processing system to detect instants in time at which a cyclically pulsating object within the body of an individual is temporarily quiescent, such an object being the heart, an artery or the lungs. The essence of the invention is the use of a doppler radar motion detector, normally used for vehicular speed detection or the detection of building occupancy. The doppler radar motion detector is arranged to transmit electromagnetic signal towards the object and receive reflected electromagnetic signal from the object, and the apparatus is further arranged to identify the instants in time at which the reflected signal indicates the object is temporarily quiescent. The invention is particularly suitable for ambulatory monitoring of the heart.