Power rings

One distinctive and recurring feature of Sonic games are the collectible golden Rings (sometimes referred to as Gold Rings or Power Rings) spread throughout the levels. This gameplay device allows players possessing at least one ring to survive upon sustaining damage from an enemy or hazardous object. Instead of dying, the player's rings are sacrificed; in most Sonic games, a hit will cause the player to lose all of their rings, although in certain situations (such as the Special Stages in Sonic the Hedgehog 2) and throughout certain games (such as Sonic Triple Trouble, Shadow the Hedgehog and Sonic Blast) a hit only costs a set number of rings rather than the entire collection. In more recent games, usually only 20 rings are now lost.
Upon colliding with a hazard, the on-screen character is thrown backwards and given a momentary period of invulnerability (represented by a rapid flashing between visible and invisible). The dropped rings burst out of the character in a circular pattern and bounce around the environment, flashing for a few seconds before disappearing entirely. During this brief period, it is possible for the player to recover some of the rings they lost. Generally fewer "recoverable" rings are displayed on-screen than the number actually lost (usually a maximum of around 20; fewer in Sonic games on 8-bit consoles, about 50 in Sonic Rush).
Certain causes of death cannot be prevented by holding a ring, including being crushed, falling into a bottomless pit, failing a mission held through a time limit and drowning.
In line with many platform games, collecting 100 of these common collectibles will usually reward Sonic with an extra life. Certain titles in the series often reward the collection of other quantities of rings, often in conjunction with the Chaos Emeralds; usually, at least fifty Rings are required to access the Special Stages in which the Chaos Emeralds may be obtained, or to utilize a character's super transformation.
The origin of the rings, like the Chaos Emeralds, is never revealed during the game series, although Sonic's Uncle Chuck, Tails, and Tiara Boobowski are shown to create rings. In addition, even Sonic characters are shown to have thought they came from a different world in official media. They are not often referenced by characters during gameplay, but they are used as currency in Chao Black Markets and in shops in Sonic the Hedgehog (2006) and Sonic Chronicles: The Dark Brotherhood. They are also mentioned to be a monetary system in Sonic Heroes. In Shadow the Hedgehog, Dr. Eggman collects them for prizes in his game-filled carnival base, and is distressed when Shadow takes them from him during the "Egg Dealer" boss battle.
Rings are also canonically equipped to characters throughout the media. To spin dash in any cartoon, contrasting to all the games, Sonic must have a power ring and can only collect one at a time. In the SatAM cartoon, Sonic also comments that the rings only last for 24 hours and work only for him. Amy and Shadow also wear rings on a daily basis, Amy probably to protect herself, and Shadow to retain his abilities (they have been with him since his creation).
*The familiar sound effect used for rings has been adopted for use in cash registers