Its not a Sone-alert, just a continuous sounding piezo (must have its own square wave generator builtin). Apply voltage and it sounds at its resonant frequency. What I need is for it to sound in a pulsing / alerting type way.

 

Ok, so you need to modify the second 555 to pulse at ~2Hz, instead of ~1kHz like I designed it. Change C2 to about 1uF.
You also need to wire your sounder red lead to sw12V and black lead to pin 3 of the second 555. Dump the output coupling capacitor.

 

ok cheers - I will have to go and grab some more components. Thanks for your patience.

 

Does R4 and C2 form a standard RC circuit that defines timing of the OUT pin ? I found a 330nF ceramic and dropped that in which slowed down the piezo.

 

Does R4 and C2 form a standard RC circuit that defines timing of the OUT pin ? I found a 330nF ceramic and dropped that in which slowed down the piezo.

The second 555 is an oscillator (astable). The timing capacitor C2 charges through R3+R4. It discharges only through R4. With R3=10K and R4=100K, the output will be close to a square wave.
Presumably, you want the tone to pulse at a couple of Hz, so make C2 even bigger.

ps. I resimed, and C2=2.2uF gives three pulses per sec. C2=4.7uF gives 1.5 pulses per sec.