An AC surge protector is a device that safeguards electronics and appliances from damaging voltage spikes, or transients, by diverting excess electricity away from connected equipment, protecting everything from home theater systems to expensive HVAC units like air conditioners from issues caused by lightning, grid switching, or internal household appliances. They work by absorbing or redirecting excess energy, preventing it from frying sensitive components, and come as plug-in strips or whole-home units installed at the breaker box, often with features like time delays and overload protection.