Found in an old publication about neon lamps this circuit works directly connected to the power grid, serving as an indicator for various situations. Ordinary neon lamps can be used.
This circuit was found in a 1965 General Electric manual. What it does is give a warning if you...
The sensor in this circuit is a BA315 diode. Other diodes can be experimented, but this is one...
This circuit turns on your car's backlight when a vehicle coming from behind gets too close to it...