The trouble with noise isn't loudness but suddenness. A cat fight outside the bedroom window or a horn honking out of nowhere jolts you into alertness. But a steady stream of sound, no matter the volume, usually isn't disruptive. And if that steady sound can mask the cats and the cars, it can help you fall asleep and stay that way.

Add white noise. "Background noise is good for two reasons," says David Neubauer, M.D., associate director of the Johns Hopkins Sleep Disorders Center, in Baltimore. "It helps block outside noises, like road-repair workers and your neighbor's stereo. Beyond that, psychologically, it’s soothing." A constant stream of low sound or a variety of recognizable ones — ocean waves, rain, summer crickets — can keep sudden noises from waking you up. Plus, some people find the sounds themselves calming.

Try… Fans, window air conditioners, or anything else that drones continuously. A sound machine is ideal if you don't want to run a fan or an air conditioner all night and if you'd rather hear chirps, croaks, or rushing water. Neubauer says the ones sold by Sharper Image are high-quality and come in a variety of sizes and price points (see Sleep Aids That Diminish Noise).

Some people also find the steady sound of music or talk radio calming when first falling asleep at night. If that strategy works for you (and doesn't bother anyone else in the room), there's no reason not to use it, says James B. Maas, Ph.D., a professor of psychology at Cornell University and a coauthor of Power Sleep (Perennial Currents, $13, www.amazon.com). But it's important to use a radio or a CD player with a timer, he says, so the noise shuts off within an hour or so and doesn't wake you later, during lighter phases of sleep.

Plug your ears. Earplugs made of soft foam or moldable silicone, which conform to the shape of the outer ear canal, are inexpensive and easy to use. You can still hear, even well enough to have a conversation, but sound is muffled and unlikely to wake you.

Try… Super Leight Pre-Shaped Foam Ear Plugs (see Sleep Aids That Diminish Noise) or Mack's Safe Sound Soft Foam Earplugs (shown; $4 for 10 pairs), both of which are available at drugstores. Roll a plug between your fingers until it's small enough to slip gently into the outer ear canal; it will slowly expand to fill the space.