An apparatus, the apparatus comprising: a wearable item configured to be placed at least partially against a skin of a person, the wearable item comprising a recess; a first optically sensitive detector mounted to the wearable item in the recess and configured to detect a sequence of optical signals from optical signals reflected from the skin of the person, the sequence comprising motion artifacts that represent a relative motion between the wearable item and the skin of the person, wherein the first optically sensitive detector is mounted to the wearable item in the recess such that, when the wearable item is placed against the skin, there is a predetermined air space between the first optically sensitive detector and the skin of the person for the first optically sensitive detector to avoid direct skin contact such that the optical signals need to travel through air; a second optically sensitive detector mounted to the wearable item and configured to detect, by using blood oximetry, a sequence of heart pulses optically from the blood circulation system of the person, wherein the second optically sensitive detector is mounted to the wearable item such that there is a physical separation between 0 and 10 mm to the first optically sensitive detector such that the motion artifacts detected by the first optically sensitive detector from the optical signals characterize also motion artifacts experienced by the second optically sensitive detector, and a processing unit configured to apply the sequence of the detected optical signals to the sequence of the detected heart pulses such that the motion artifacts are reduced from the sequence of the detected heart pulses. a wearable item configured to be placed at least partially against a skin of a person, the wearable item comprising a recess; a first optically sensitive detector mounted to the wearable item in the recess and configured to detect a sequence of optical signals from optical signals reflected from the skin of the person, the sequence comprising motion artifacts that represent a relative motion between the wearable item and the skin of the person, wherein the first optically sensitive detector is mounted to the wearable item in the recess such that, when the wearable item is placed against the skin, there is a predetermined air space between the first optically sensitive detector and the skin of the person for the first optically sensitive detector to avoid direct skin contact such that the optical signals need to travel through air; a second optically sensitive detector mounted to the wearable item and configured to detect, by using blood oximetry, a sequence of heart pulses optically from the blood circulation system of the person, wherein the second optically sensitive detector is mounted to the wearable item such that there is a physical separation between 0 and 10 mm to the first optically sensitive detector such that the motion artifacts detected by the first optically sensitive detector from the optical signals characterize also motion artifacts experienced by the second optically sensitive detector, and a processing unit configured to apply the sequence of the detected optical signals to the sequence of the detected heart pulses such that the motion artifacts are reduced from the sequence of the detected heart pulses.