Magnetic circuit breakers are made of electromagnets; their strength is determined by the amount of current flowing through the circuit breaker. When a power surge occurs, the large amount of current strengthens the electromagnet enough to influence a lever to part the contact plates that had completed the adjoining circuit.
Thermal circuit breakers use the influence of heat on a bimetallic strip -- two different metal strips, joined together -- to discontinue a circuit in the event of an abnormal current. Excessive current causes an increase in temperature that influences the two metals differently, due to their different expansion rates. One of the contacts of the bimetallic strip bends away from the other, causing the circuit to be interrupted.
A combined thermal and magnetic circuit breaker is a special type of circuit breakers that posses properties of both magnetic and thermal electric breakers. It has an electromagnet designed to react to sudden fluctuations in current and a bimetallic strip to prevent damage from a prolonged overload in the circuit.
Ground fault circuit interrupter (GFCI) breakers protect people around electrical equipment, especially equipment used around water environments. They are capable of detecting grounding of the current due to water. Most modern houses are equipped with GFCI breakers for the safety of the residents.