The sparks can go up to 0.6 cm, you can upgrade it with increasing input voltage
Step 1: Modifying Electric Swatter
Just open up your electric swatter, and you will find the circuit like at the photo,and remove the big red capacitor like I show you in the photo
Step 2: Time to Desolder the Capacitor
Desolder the one big red capacitor, on other side, that is cable going to output volt, so keep that mind the polarity, after you desolder the capacitor, resolder the cable output, thats gonna be the high voltage output
Step 3: Time to Play It!!!
Put the input voltage between 1.5 volt to 9 volt, keep that mind if you put input voltage above 3 volt, don't turn on too long or you will burn the transistor and the voltage multiplier, have fun with it, in the photo I'm using 4 aa duracell battery and it's fully functional working... Have fun ...