Abstract: An alarm system comprises of a closed circuit includes an alarm cord connected to a DC power source, a disconnect signal detector having an inverter circuit and a thyristor and a push-button switch. An alarm generator produces an alarm sound by the detection signal from the disconnect signal detector. A first charging-discharging circuit is connected to the DC power source through a first transistor which is turned on when the push-button switch is depressed, and a first Schmitt trigger circuit transmits a connect signal to the disconnect signal detector only for a time period set by the first charging-discharging circuit. The Schmitt trigger circuit transmits a disconnect signal to the disconnect signal detector after the setting period determined by the first charging-discharging circuit.