If you don't have a Piezo sounder with integral oscillator to hand or you want greater
volume, then this simple circuit can be used as a replacement for the Piezo sounder.
This circuit is based on the popular 555 timer and runs from a 12V supply,
the two transistors provide a simple interface from the TTL level logic of the PIC.
By gating the 555 via the reset input of the 555 oscillation can be controlled.