555 NOISE BUTTON/ OP AMP
Pin 5 of a 555 is usually 2/3rds of the 12V supply which is +8V. You can force it up to 11.6V and force it down to 4.4V. The output of the left side 555 driving yours forces it up to +10.7V and down too far to almost 0V. So attenuate the 0V to +10.7V down to 0V to +7.2V and capacitor-couple it into pin 5 of the frequency shifting 555.

Then the output level from the siren 555 will be WAY TOO LOUD and it will need its own volume control.