I read the replies below. The ones that suggest unplugging the system from the building power during storms are good advice. A surge protector is what we normall see as what is called a Power Tap (a string of outlets on a single molded housing with one cord oing to the wall in which you can plug several electronic items like computers or TV etc. Many times they also have telephone jacks on them to protect your phones or modems.
Power taps mayalso be in the form of unit that might sit under you laptop or look like like a thin table top unit. But they all employ the same methods of protection. First remember - surge protection is not the same as lightning protection. If a multi million volt bolt of lighting hits directly to your system via phone or power lines - you can kiss it goodbye - no little on-off switch or MOV or choke coil is going to stop it. It will jump everything and head for the path of least resistance which Murhpy says willbe you best equipment - So ---- in severe lightning storms - dont kid yourself - unplug the stuff - end of story.
Surge supressors are intended to protect sensitive equipment from occasional surges - not lightning strikes. Surges occur constantly from what are called inductive kickbacks or in electronic terms Reverse EMF voltages. A refrigerator turns off or on - the motor starts - the lights in the house dim a litle from the surge required to start the motor - and when it starts a reverse EMF of as much as 1000 volts can kick back through your home wiring. Compressors, furnaces - even theneighbors equipment if it is on the same pole transformer - can throw surges into your home. storms a mile away can do it also. These surges are constant - every time a light is turned on (minor surges) to a large motor on a compressor (IE) will toss spikes into the wiringin your house. If oyu were to monitor your electrical lines with an Oscilloscope you would be hard pressed to find any 2 minute interval where a surge DOESN''T occur. They are everywhere.
The surge protector removes or "suppresses" these surges - that is if the voltage is 120 Volts AC to your system and a surge of (IE) 400 volts barrels down the line - the surge protector will catch it in nanoseconds and basically short it out - that is sync it to ground. Surges can occur between the hot neutral wires (black and white) the hot and ground (black and earth ground or green) or neutral and ground. Hence the surge protector need 3 components to protect a normal home wiring system. So one is placed across each of those three pairs effectively shunting surges across any of the pairs and only permitting 120Vmax to reach your computer.
The surge protector most commonly used is the MOV - or Metal Oxide Varistor. It is much like a thyristor or zener in that it will not operate at its rated voltage but if a voltage larger that it is designed to accept hits it - it goes into what's called the "avalanche" mode - that is - it instantly becomes a near short circuit - shunting for the one or two cycles of that surge and effectively passing it around thesystem. It will heat up of course but its such a short duty cycle that it doesnt normally overheat. These can take repetitive hits of surging and reset instantly. If you ever look inside the unit you will see these - they look normally like small round candies - red or black normall - with 2leads from them to each of the pairs needing protection. On a cheap protector like a $10 one from a hardware store - if you opened it - you would seejust 3 MOVs - right where the power cord enters but after the on-off switch. - Putting these at the head end of the power line - protects everything down stream. In fact I make these for mobile use. I take a larger power plug from a hardware store and wire these into it and seal it. If I am connecting to a power outlet somewher and want protection - I simply plug the MOV plug I made into one of the duplex outlets and the computer or other item into the other outlet - then it isprotected - assuming they are both on the same circuit.
More expensive protectors have more sophisticated protection - using separate MOVs on each outlet - and adding choke coils (wound coils that will "choke" the surge inductively. There are also very sophisticated ones that use complex circutiry that captures the surge and sets off alarms and such. But the MOV is the standards - is as fast as anything on the market. But
remember---- it cant stop a lightning strike -s o unplug in storms. There are ways to test the MOV but thats another story - in case you are concerned it isnt protecting. Best if you doubt is to just buy a new one if its cheap - otherwise have a qualified electronic technician - test yours. Its a simple matter of raising the voltage to each MOV and scoping its response to that higher voltage. Hope this helps.
