conductivity tester, handheld device provides a qualitative visual indicator of the conductivity of different solutions, acids or salts, Two brass probes can be touched to a solid substance, or immersed in a liquid, to show conductivity on green LEDs
Energy Tube, teaching resource for an array of scientific concepts: open and closed circuits, conductors vs. Insulators, light waves, sound waves,currents, and energy, When a conductor touches both of the electrodes on tube, tube emits a sound and flashing red/green/blue LED lights