A reflectance pulse oximeter for detecting pulse synchronous waves is disclosed. The detector includes a sensor or sensors for detecting physical motion of the subject so that readings influenced by subject movement can be eliminated or indicated. One form of motion detector used is an accelerometer employing a spring-supported weight mounted within a cylinder. Accelerations beyond a predetermined value cause the weighted member to complete a circuit against the inside walls of the cylinder. Three accelerometers for detecting acceleration in each of three directions can be utilized. Motion can also be detected by a cubic motion detector having individual reed valves associated with each of six faces. A magnetic ball is movable in a spherical space formed within the cubic body. The magnetic ball operates to actuate only one of the reeds which is at a time. Motion detection can also be accomplished by a combination of the cubic motion detector and one or more accelerometers of the type previously described. A microprocessor control system determines the presence of a pulse synchronous wave from the reflectance detector system and can suppress indication of a pulse synchronous wave occurring simultaneously with motion detection by the motion detecting sensors, which motion is detected for greater than a predetermined period of time. The control system also can include provision for the display of an indication that the displayed pulse synchronous wave occurred during movement of the subject.