When it comes to decorating for Halloween, any soccer mom can run to the local big box and grab a light-up skeleton or animated rat — but any mad scientist worth his Bunsen burner knows a Jacob’s Ladder is the way to go. They look cool and they sound cool, and you can build one for next to nothing from scrounged materials.
An ignition transformer from an oil furnace forms the heart of this unit. For those Toolmongers north of the Mason-Dixon, this is the time of year people are getting their furnaces serviced — call your local shop and ask if they have any transformers they’ve removed. If you don’t live in oil-furnace land, you can substitute a neon sign transformer.
Most importantly, remember that you’re dealing with 10,000 volts or more. That kind of juice demands respect, so be safe.
Jacob’s Ladder [instructables]