Automatic and open-heart skeleton watches: spring-driven, self-winding through wrist motion, no battery needed. Mechanical watches usually gain or lose a few seconds a day, more than quartz, and benefit from regular servicing. If you do not wear one daily, it will stop once its power reserve runs out; wind it by hand or wear it again and reset the time. Keep it away from speakers and magnets, which can make it run fast. See our automatic vs quartz comparison.