New rules for duty-free shopping

If you're used to buying a bottle of single malt scotch at a duty-free store and schlepping it home from Europe, you may have to change your habits. The U.S. Transportation Security Agency (TSA), the European Commission, and the British have adopted consistent rules for carry-on liquids that make it easier to take small amounts of liquid onboard, but make duty-free imports more difficult.

Here are four rules that control what you can and can't do:

• Any liquids you carry onto a flight must be in a container of less then three ounces or 100 ml (about 3.3 oz), you must pack any such containers into a one-quart/one-liter transparent plastic bag (such as Baggie or Ziplock), and you have to run the plastic bag separately through the screening machinery.
• Standard liquor bottles are OK as carry-on only if you buy them in a secure airport area, after you've passed through screening.
• When you arrive back in the U.S., you usually have to leave the secure area and claim your checked baggage to go through customs and immigration. If you have a connecting flight, you have to reprocess through screening, where the regular carry-on limits apply.
• You can transfer a bottle from carry-on to a larger bag while you're in U.S. customs before you re-check it. However, if you arrive from an airport with U.S. pre-clearance (Aruba, Bermuda, Freeport, Nassau, and seven large Canadian airports), you do not have access to your checked baggage and can't make a transfer.

Taken together, these rules mean that you can buy your bottle in the duty-free shop when you leave a foreign airport, provided the shop is in the secure area. If you're on a nonstop flight to your final U.S. destination, you have no further problem. However, if you take a connecting domestic flight, security will not allow that bottle in the cabin of your connecting flight. The only way to get it on the second flight is to repack it in a checked bag.

As far as I can tell, the process works the same way if you're going overseas. If your first airport is your final destination, you're OK with a carry-on you buy from a secure-area store, but if you take a connecting flight, the bottle has to be in a checked bag.

Of course, you can also buy bottles, anywhere, as long as you put them in your checked bag. (And then hope nobody bashes your bag hard enough to break the bottles.)

This development is as good an excuse as any to refresh the record on duty free. You need to know two basics:

• The "duty" you avoid is the tax imposed in the country where you buy the merchandise, not the U.S. Duty free or not, what you buy outside the U.S. is still subject to U.S. customs. But the U.S. allowance is generous.
• Most duty-free airport stores now adjust their prices to be just slightly below open-market prices and pocket the extra markup. Only a few airports (Dubai, for example) price duty free as low as possible.

In my experience, duty free is a good deal for travelers who live in countries with high value-added taxes on consumer goods—and that includes almost all of Europe. Europeans routinely buy lots of duty-free stuff in airports and they frequently head for tax-free areas such as Andorra to buy consumer goods.

Duty free is generally not a good deal for residents of the U.S., where tariffs on imported goods, merchandise taxes and retail markups are low by world standards. Over the years, I've found that liquor and tobacco represent the only consistently attractive duty-free items, since they're among the few items the U.S .taxes heavily. And even then, most duty-free airport stores price those items to be just slightly cheaper than at home.

Clearly, I'm not a great fan of duty free. But if you are, take note of the rules, and plan your trips accordingly.