A GFCI circuit breaker is primarily designed to detect:

A Ground Fault Circuit Interrupter (GFCI) circuit breaker is specifically designed to protect people from electrical shock by detecting current leaks to ground. The fundamental operation of a GFCI relies on monitoring the current flowing through the live (hot) and neutral wires of a circuit. Under normal conditions, the current in these two wires should be equal. If there is any discrepancy, meaning some current is leaking to the ground, the GFCI will trip and cut off the electrical supply almost instantaneously.

This is crucial in environments where water is present, such as kitchens and bathrooms, where the risk of electric shock is higher. By detecting these current leaks, GFCIs help prevent serious injuries and fatalities due to electric shocks.

Other choices do not accurately describe the primary function of a GFCI. While overcurrent protection is provided by standard circuit breakers, voltage spikes are typically managed by surge protectors, and high resistance errors would not directly relate to the specific operation or design purpose of a GFCI, which centers around ground fault detection.