The sweep alarm circuit using 555 IC is a very simple circuit, which can be used to make alarm sound.
In the circuit, when supply is given, IC 741 produces a variable voltage and the variable voltage is given to the voltage control pin or 5th pin of IC555. When it receives a voltage, the IC starts to function as a Astable Multivibrator. SO, the IC 555 starts to deliver clock pulses with a frequency for a particular time, which is designed by the formulae shown below. This clock pulses are given to the Loud speaker. According to the pulse received, the Loudspeaker alarms from high sound to low sound and vice versa. As the sound sweeps, this circuit is named as sweep alarm circuit.