Which device monitors current to trip a circuit if there is an imbalance?

The Ground Fault Circuit Interrupter (GFCI) is designed specifically to monitor electrical current and detect imbalances between the incoming and outgoing current flowing through a circuit. When it senses a difference, which could indicate a potential electric shock hazard (such as current leaking through a person's body to the ground), the GFCI quickly trips the circuit to prevent injury or damage.

In contrast, other devices like fuses and circuit breakers protect circuits by interrupting the flow of electricity when a circuit is overloaded or a fault occurs, but they do not specifically monitor for ground faults or imbalances. A surge protector, on the other hand, is used to protect devices from voltage spikes but does not monitor current in the same manner as a GFCI. Therefore, the unique function of a GFCI to specifically monitor current imbalances makes it the correct answer for this question.