What you need:
- an arc lighter or any flyback transformer which can reach 3KV/millimeter with a frequency ranging from 36 to 40 kilohertz.
-any pair of headphones.

For EXTRA LONG RANGE
-a flyback transformer from a CRT monitor (or anything bigger) of 30KV modulated at the same aforementioned frequencies.
-a loudspeaker, the bigger the better.

As you may expect, it follows the square law proportionally. Feel free to scale it as you please, according to your needs.