There are two sockets on these products. By plugging a phone line through the sockets, you can minimize the effects of a surge coming into your equipment through the phone line. Facsimile machines, cordless phones and answering machines are especially sensitive, and computers with internal modems can be completely destroyed by spikes on the phone line. A Suppressors are usually devices that plug into the wall outlet and can handle surges up to 6,000 volts. Arresters divert excess energy to the ground, reducing voltage surges to a level that can be handled by your electrical system and surge suppressors located downstream from the electrical panel.
Many manufacturers misrepresent their products.
Some claim a UL listing for their products if they use a single UL listed component such a the power cord. Other products have never been tested as anything more than a Temporary Power Tap, UL's term for an extension cord. A Ten percent of the purchase price of a solid state system is a good value to use for insurance against power disturbances.