What you need:
1 Ooga horn ($9.00 Harbor Freight)
A length of two conductor wire
1 Pumpkin (~$5.00 Walmart)
1 12V power source (Battery or Adapter with high amp rating)
Some Trick or Treater's
This is really easy so I will explain it step by step.
Acquire a fairly large pumpkin.
Make sure that your pumpkin is carved but not in a way your victims can see your horn.
Connect a long wire to the Positive and Negative Terminals of the Ooga horn.
Cut a small hole in an inconspicuous part of the pumpkin.
Push the wire through the pumpkin from the inside.
Place your horn inside your pumpkin.
Pull your wire to a hiding place where you can see the targeted area and your victims cannot see you
Have a 12 Volt power source ready as this will power the ooga horn (I use a 12V APC battery)
Firmly connect the Positive lead from the horn to the Positive terminal on the battery.
When ready to frieghten people simply touch the Negative Lead from the Horn to the Negative Terminal on the battery.