Money belts are worn under your clothing to protect your valuables: typically cash or traveler's checks. You can also use them to carry your travel documents if you'd rather not leave them in the hotel safe.
The type of money belt you choose depends on what items you'll carry in it. If it's strictly for cash or other pliable and small items, consider a belt that is worn around your neck and dangles like a necklace beneath your shirt and below your bra line. This won't interfere too much with your profile and is relatively invisible. If you're carrying bulkier items, consider one that is worn around your midriff under your clothing, so that you can keep a stiff passport or similar item in the pouch and carry it in the small of your back. If you have something of particular value or simply want an emergency stash, consider a money belt that places a pocket in your bra (see Resources below). You can also buy a simple belt that has a pocket in the lining if you want to carry a large denomination bill as emergency cash.
Money belts do provide peace of mind, but don't be too relaxed. Thieves know about money belts. And women are particularly vulnerable because of their relative lack of strength and size. If a thief is desperate enough to rob you, he's also desperate enough to cause you injury while trying to grab your money belt. Don't fight; money isn't as important as your safety.
Money belts can be bulky and uncomfortable. Most are designed to be worn by men, so they aren't particular fashion-enhancing when worn under women's clothes. They typically include a 14-inch pocket and are made to fit waist sizes of 32 inches and larger. Because they're also made of all-weather material, they can get sticky and hot worn under your clothes and right next to your skin. Airline tickets have also been known to smudge and smear in this manner, rendering them unusable for the return home. Money belts can also be pretty obvious when you have an odd-shaped lump beneath your clothes and a string hanging around your neck.
Money belts sound like a terrific idea for most women, until you've climbed to the second tier of the Eiffel Tower in June. You're hot, sticky and the belt is making you itch. Not to mention that the bulk of it is making you look as if you might be in your first trimester of pregnancy. A better solution is to have small pockets sewn into your undergarments into which you can stash a bit of money, and use the hotel safe for the remainder of your cash and any travel documents.