You plug in the hair dryer, and the light flickers. Or maybe your TV screen wavers when the air conditioner kicks on.

These are the electric surges that can damage your electronic equipment—and the very thing surge protectors are designed to filter.

Chances are good you have a bunch of electrical items plugged into a multiple-outlet device of one kind or another. But the thing you bought to protect your computer may not actually have the power: There’s a difference between power strips, which simply add to your outlet’s capacity, and surge protectors, which actually block electrical surges from reaching your equipment.

A surge protector works by diverting the extra power to a grounding wire, which means that it’s not going to do its job unless you plug it into a properly grounded outlet.

You don’t necessarily need that protection for a toaster or alarm clock; however, for intricate electronics like computers, media centers, and even fancy kitchen appliances, a surge protector can stave off the damage from surges, which can not only wear down but also destroy these items.

Interestingly enough, once you get a surge protector, you aren’t in the clear forever. A 1,000-joule surge protector can take up to 1,000 joules of surge—usually in many smaller “hits” of power. You can buy surge protectors that warn you when they’re wearing out, but you probably also want to switch out your surge protectors after you know there’s been a big power event, like a blown transformer in your area.

Many surge protectors even give you a warranty on whatever you have connected to their product.

And here’s one more bonus: You can use your surge protector to cut off the electricity to several items at once that may be pulling power even when they aren’t on—like cable boxes, televisions, or game systems—and see your savings . . . surge. Yep.