An apparatus for determining a pulse wave signal representative of vital signs of a subject is disclosed. The apparatus comprises a control unit, a first sensor coupled to the control unit and configured for emitting a first signal indicative of a pulse wave of a subject, and a second sensor coupled to the control unit and configured for detecting motion the apparatus is subjected to and for emitting a second signal based on the detected motion. The control unit is configured to receive the first signal from the first sensor, to determine a pulse wave signal based on the first signal to receive the second signal from the second sensor, and to determine a reliability signal based on the second signal. The reliability signal is indicative of a reliability of the first signal.
