The invention relates to a Doppler radar heart sensor comprising a radar signal emitter (102); a radar signal receiver (103); a signal pattern matcher (106); and a transmission power adjuster (108). The signal pattern matcher (106) is connected to the radar signal receiver (102) and arranged to analyze a received radar signal (105), to compare the received radar signal with signal patterns, and to issue a corresponding indication signal upon detection of a sufficiently high similarity between the received radar signal and at least one of the signal patterns. A transmission power adjuster (109) is connected to the radar signal emitter (102) and the signal pattern matcher (106), the transmission power adjuster being arranged to gradually modify a transmission power delivered to the radar signal emitter (102) until the signal pattern matcher issues the indication signal. The invention also relates to a corresponding method and a computer program product.