Neon is a gas.
Neon gas can be used inside light bulbs.
Neon gas light bulbs can be used directly as voltage testers.
Neon gas light bulbs can also be used as indicators in other types of electrical testers.
Not all "voltage" testers actually measure voltage directly.
Current is not voltage.
Your question, as currently asked, forces the reader to make too many guess about what you really want to know. That is why you are not getting any useful answers.
That, and you are asking mechanical engineers about electrical stuff.