Wearable devices are described herein including at least two photodetectors and a mount configured to mount the at least two photodetectors to an external surface of a wearer. The at least two photodetectors are configured to detect alignment between the wearable device and a target on or in the body of the wearer (e.g., to detect the location of vasculature within the body of the wearer relative to the at least two photodetectors). Alignment of the at least two photodetectors relative to the target could enable detection of one or more physiological properties of the wearer. For example, the wearable device could include a sensor configured to detect a property of the target when the sensor is above the target, and alignment of the target relative to the at least two photodetectors could include the sensor being located above the target.
