A friend told me this story many years ago: He was working on repairing some electronic staff and one block had a green light turned on when the block was turned off by a switch, but not disconnected from the power line. However, there are no short circuits in it. After long investigation, mostly for curiosity, he found that some piece of alloy covered another piece and together they created a capacitor, which was able to let in AC part of incoming signal and power the light in the gadget.
A friend told me this story many years ago: He was working on repairing some electronic staff and one block had a green light turned on when the block was turned off by a switch, but not disconnected from the power line. However, there are no short circuits in it. After long investigation, mostly for curiosity, he found that some piece of alloy covered another piece and together they created a capacitor, which was able to let in AC part of incoming signal and power the light in the gadget.