This alarm siren circuit give continuous frequency sweep, a warbling sound. The warbling period is about 6 seconds, 3 seconds for frequency sweeping up and 3 seconds for frequency sweeping down. You can change the warbling frequency of this alarm siren by changing the C1 capacitor value. You can vary the value between 10 uF to 47 uF and get an interesting effects. Here is the schematic diagram of the circuit:
This alarm siren circuit works with 5-15V voltage source, but I recommend 5-9 volts as the best result. Above 12 volts, the 555 IC would suffer self-heating and this may shorten its lifetime. Finally, this alarm siren is simple and there would be a lot of fun to make it works.