Automatic watches are powered by the natural motion of your wrist while you wear them. This type of watch has a rich history reaching back to the 18th century. Today, countless brands produce their own automatic calibers for their watches.
Automatic watches fall under the larger umbrella term of mechanical watches. They offer a key advantage over manual timepieces: They wind automatically via the movement of the wearer's arm. An oscillating mass inside the caliber is responsible for winding the spring. Today, this is in most cases a winding rotor. It is flexibly mounted so that gravity pulls it towards the center. When you're wearing the watch and move your wrist, the rotor moves and gives the caliber new energy. Automatic watches don't require batteries, making mechanical watches comparably more environmentally friendly than battery-powered quartz watches.
Automatic watches are available from almost every famous watch manufacturer in all price ranges. Less expensive models are often powered by base calibers made by the ébauche manufacturers ETA, Soprod, or Sellita. Various manufacturers use these calibers in a more or less reworked form in their watches. These calibers even power the watches made by famous brands such as Breitling and TAG Heuer. However, both manufacturers have developed their own in-house movements as well.
Rolex and Patek Philippe are some of the most well-known watch manufacturers. Unlike many other brands, these two Geneva-based manufacturers don't outsource base calibers. Instead, they use their own. For example, Rolex's caliber 3130 is considered very robust, reliable, and precise. These qualities and more make the caliber one of the best automatic movements on the market; it powers Rolex watches such as the Submariner. Since Rolex produces their watches almost entirely in-house, production is costlier. This results in higher prices for automatic watches with in-house movements.