If you want to test a radiation detector, such as a Geiger counter, you need some way of generating radiation to detect. The majority of us can agree that it’s a bad idea to set off nuclear weapons in our backyards, so it’s necessary to have a gadget capable of creating a small, safe amount of radiation. There are, of course, commercial devices that can do that, but you can also build your own from a barbecue lighter.
The device is an X-ray emitter that shoots a pulse of about 10 keV of X-ray energy. That’s a very small amount of radiation, and so it shouldn’t be capable of harming you — even if you fired it repeatedly into your eyeball or something. In fact, it’s so small that the X-ray emitter doesn’t even have a power source. All of the energy needed to fire the pulse is generated by the lighter’s piezoelectric igniter. But, the pulse is still strong enough to be detected as a blip on a Geiger counter, allowing you to safely test the equipment.
Other than the barbecue lighter itself, you’ll only need a vacuum tube and a large diode. Vacuum tubes are able to create X-rays (along with much of the rest of the spectrum) when a very large voltage is applied to them. However, that doesn’t require much current, which makes a piezoelectric igniter a perfect power source because they produce a high-voltage low-current arc by design. If you want a safe way to experiment with generating X-rays, this is a great low-cost option.