The current invention is an automatic AC power interruption system built into a portable apparatus or integrated into electrical systems and appliance control circuitry. Power is interrupted in potentially hazardous conditions, for example, when a T3 smoke detector alarm signal is detected. Alternatively, a portable device may be plugged into a power outlet having a GFCI breaker and, when a hazard alarm condition is detected, trip off power to the outlet. Signal-activated circuit interrupters (SACIs) may be integrated into appliance control circuitry and interrupt power to a problematic device when a hazard alarm condition is detected. In addition to fire prevention, other hazard alarm conditions may include alarms indicating toxic fumes, motor overload, natural gas, radon, or carbon monoxide. Interconnected networks of signal-activated circuit interrupters are also disclosed.