A pulse oximetry device is provided that fixates generally around a user's wrist. The device may include one or more mechanical features that fix the device at, for example, a distal end of a wearer's ulna bone. The device may include one or more projections formed from a suitable material (e.g., elastomer such as silicon) that cause the device to fit snugly against the wearer's wrist and remain in place even when the wearer is moving, thus reducing motion artifacts in signals detected by the device. The device may include one or more mechanical features or fins that reduce ambient or stray light in the measurement area. The device may include one or more detectors, and one or more light sources, each having a different axis resulting from the manner in which each is angled toward a virtual center point of the distal end of a wearer's ulna bone.