A circuit breaker is a crucial safety device in electrical systems that monitors the flow of current through a circuit. The circuit breaker trips when the current exceeds safe levels, such as during an overload or short circuit. This mechanism activates an internal switch, either through a thermal or magnetic mechanism, that breaks the electrical connection and stops the flow of electricity. By interrupting the current, the circuit breaker prevents any damage or potential hazards that could occur due to excessive electric current.