It uses IC timer NE555. When the circuit at its close state, the IC will control the buzzer time using the resistor and capacitor. The buzzer sounds like alarm in the different frequencies.
Resistor R1 : 1.8k ohm
Resistor R2 : 1k ohm
Resistor R3 : 5.6k ohm
Resistor R4 : 480 ohm
Capacitor C1 : 2.2 nF
Polar Capacitor C2 : 0.022uF/6V
IC1 timer : NE555
Speaker SP1 : Tweeter 8 ohm
Power supply : 5V
