A ring includes an inner surface configured to contact a finger of a user when the ring is worn by the user. The ring can include a first power source configured to be wirelessly charged by a second power source that is (i) removably coupled along a circumference of the inner surface of the ring, and (ii) disposed at an outer surface of the ring. The ring also can include a sensor configured to draw energy from the first power source and sense an activity of the user wearing the ring.
