This is simple siren circuit diagram that build easily. Because of use the transistor 2 pcs only just. Can use 8 ohm size loudspeakers. Which , I uses old loudspeaker , at the sound doesn’t Amen! come to usable with this comfortable circuit. The usability just you presses switch (close) S1 a loudspeaker will utter. Enhance the frequency goes up (C1 , loaded ). When liberate Switch(Open)S1. The sound will decrease the frequency down (C1 , disgorge load ) change the value R1. For change the time goes up – down. Please see circuit picture assembles.