The Siren tone generator circuit using 555 circuit generates a siren sound, which can be used as a alarm. As the siren sound is a most ear catching sound, it is used for security purposes.
SA is the Activation Switch. When the supply is given, IC555 gets triggered. IC 555 is connected to work in astable mode, using R1, R2 and C1. When there is a pulse received from 555IC, there will be an siren audio heard from the Loud Speaker.