The Circuit Breaker is a small and simple PCB designed to detect a short circuit and immediately cut off the power. Power is reinstated after 5 seconds, if the shortcircuit is gone.
The Circuit Breaker cuts power under 5ms. This makes the Circuit Breaker faster than any booster or DCC central. It is in fact so fast that you hardly see trains blink with their lights when an other train is causing a short circuit.
The main idea is to prevent a short circuit from disabling your entire layout. So when a train derails and causes a short circuit, the Circuit Breaker will prevent the rest of your layout to be affected. This is usefull for large layouts to locate derailments more easily.
In order for the Circuit Breaker to work, you will need to use a lot of them. It is best to arrange these so that only one train will be behind a Circuit Breaker at any time. The Circuit Breaker also lights up a red LED to indicate that there is a short circuit.