it's very cheap, like 10 bucks or less.is a shock machine, its very funny to put to max level and see the face of the other guy.
its high voltage but low current (it's like 40 v .5 Amp)
Step 1: Components
1 Variable resistor 100 K
1 Transformer for 12 V with central derivation
1 NPN transistor TIP31C
1 Resistor 560 OHM
1 or 2 battery clip (for 4 AA batteries)
4 AA batteries
2 Copper tubes
a lot of wire
Step 3: Thats it !!!
if you take it to school you can win a lot of $$$ money $$$!!!