Varistor
Why are they used?
The varistor is a surge protection device that is connected directly across the AC input. When a power surge or voltage spike is sensed, the varistor's resistance rapidly decreases, creating an instant shunt path for the over-voltage, thereby saving the sensitive control panel components.
Applications / How do you spot opportunities?
Cellular phones, data transmission lines, LANs, modems, etc
How to ask for opportunities?
Do you need any device to control the abrupt voltage fluctuations of a circuit?