We wrote about the opening Monday of three local centers where people can apply to join the Transportation Security Administration’s Pre-Check program, which lets fliers keep their shoes, belts and sweaters on and not have to pull their laptops from cases or display their bags of liquids in special airport checkpoint lines.

Several readers had questions about Pre-Check and another program, Global Entry.

Orhan writes: “How different are these programs? Are they the same, or 2 different programs? Is one international including domestic, the other just domestic? Or of you need to apply for both? Can’t seem to get simple answer from websites.”

Pre-Check is a TSA program in conjunction with nine major airlines that allows people to pass through expedited security lanes at more than 100 U.S. Airports. Global Entry is a program of the U.S. Customs and Border Patrol that is intended for frequent international travelers. It costs $85 to enroll in Pre-Check and requires U.S. citizenship or proof of legal residency. Global Entry costs $100 and requires that applicants hold a passport.

You are eligible to use Pre-Check “fast lanes” at U.S. airports if you are a member of either Pre-Check or Global Entry.

If you plan international travel, Global Entry is the better choice because it allows for expedited clearance when you return to the United States.  Participants may re-enter by using automated kiosks. They present their machine-readable passport or permanent resident card, put their fingertips on the fingerprint verification scanner, and make a customs declaration. The kiosk issues a receipt and directs the traveler to baggage claim.

John wonders: “Are there  any [Pre-Check] centers planned for D.C. or already opened?”

At this point, no word that they plan to open one.

You can register for Global Entry in town, however. The downtown enrollment center — at 1300 Pennsylvania Ave, NW, in the Ronald Reagan Building — is open Monday-Saturday, 7 a.m. to 7 p.m.

The three Pre-Check centers that opened Monday are in Alexandria at 3139 Duke St., below the Lone Star Steakhouse; in La Plata, Md., in the White Plains Corporate Business Park, 10665 Stanhaven Pl., Suite 300A; and in Dundalk, Md., at the Point Breeze Business Center, 2200 Broening Hwy., Suite 110.