What are some plasma ball tricks?

Plasma ball tricks take advantage of the tendency of electrons to flow out of the partial vacuum of the glass sphere, through any conducting object touching the surface and to the ground. These electrons affect any unshielded instrument, such as a digital watch or fluorescent light bulb.

When a digital watch is placed on the glass of a plasma ball, the numbers will change because of the electric field, even if there isn't a battery inside. The power is being provided by the flowing electrons, which are trying to become grounded by flowing through the device. This same effect will cause a light display in a disconnected gas discharge tube touching the glass sphere.