The present invention discloses a security apparatus and method using the AC power line signal for the sensor. According to the present invention, is installed inside the building detects the intrusion and a plurality of sensor unit for outputting a detection signal, the first alternating current signal or the AC transmitter for selectively outputting a second AC signal, and the alternating current according to the intruder detection is connected through the first AC signal or the third sensor unit and the two wires of the first transformer to a signal comprising a first transformer that transmits through the two wires comprising a second alternating current signal to the transmitter output, using the third signal of the first alternating signal and the second to detect the AC signal through a security device comprising a premises security device for determining whether intrusion exchange the power supply line of the two-wire signal from said first transformer is transferred It should be able to deliver the power and the sense signal at the same time to. The same is easy according to the present invention enables the power supply and signal transmission lines by using two wiring and wiring, and to reduce the wiring cost. Security systems, an AC signal, 2-wire