You're staring at the computer screen. The air conditioner comes on and then abruptly shuts down. Your monitor flickers for a few seconds. Poof! Suddenly the numbers on that cost estimate have vanished. You've just been struck by dirty power.

Dirty power is any electrical current that varies by more than 10% from the
usual 120 volts. Power spikes, surges, sags, and brownouts can destroy data on your computer and sometimes even ruin expensive equipment. That's disastrous when it's your gear.

To guard your data from dirty power, plug everything (computer, monitor,
speakers, printer, modem) into a surge protector. Companies such as
Kensington Microware build reliable surge protectors that safeguard systems from minor power annoyances. Kensington's latest offering are its
SmartSockets protectors, which look like power strips with color-coded outlets. Depending on the model, they can handle power-adapter plugs and range in price from $20 to $50.

When a falling tree cuts off power in your neighborhood, however, a surge
protector won't protect your computer. (The same goes for brownouts.) For that you need a UPS, or uninterruptible power supply. Computers such as the NEC system reviewed above come bundled with a UPS, which will sustain your system for a couple of minutes while you save active files.

If you have your own Web site or are the frequent victim of power outages, you need better protection. A UPS with about a 1,000 volt-ampere (VA) rating will do the trick. I recommend American Power Conversion's $699 Smart UPS-1000, which can handle the load from a computer for 25 minutes. The company has just introduced software that lets you check on the computer's status over the Web, so you never need wonder whether your system is running when you're on the road.

Coordinates SmartSockets, Kensington Microware, 800-535-4242,
www.kensington.com; Smart UPS-1000, American Power Conversion Corp.,
800-877-4080, www.apcc.com

Fast Company