Here’s Why the U.S. Is Banning Larger Electronics on Some Overseas Flights

The Trump Administration’s new ban on carry-on electronic devices on some international flights has left many wondering why certain devices and airports are being targeted, and why carry-on and checked luggage are treated differently.

Passengers traveling on foreign airlines to the U.S. from 10 airports in eight majority-Muslim countries will be required to place all personal electronic devices larger than a cell phone into checked bags. That includes laptops, tablets, iPads and electronic games. The rules took effect Tuesday, and airlines have 96 hours to implement them.

TIME spoke to aviation security experts about the reasoning behind the rules. Here’s what you need to know:

Why ban laptops and not cell phones?

The Department of Homeland Security directive, which did not reference a specific credible threat, mentioned a February 2016 incident in which an explosive device in a laptop blew a hole in a Somali passenger jet, forcing an emergency landing. One person, the suspected bomber, was killed. Experts reached Tuesday said smart phones don’t pose the same kind of threat.

“This is a world in which size matters,” said Bennet Waters, a counterterrorism expert at the Chertoff Group who served in the Department of Homeland Security.

He referenced the TSA rule that limited the volume of liquid passengers could bring on a flight, concluding that “within certain quantities and if contained in certain ways, liquids, creams and gels did not pose a threat to commercial aviation. But in quantities above that, they might.” Waters said the same logic applies to small smart phones, compared to larger laptops and tablets. “The bigger the device, the more you can get in there,” he said.

Why ban carry-on devices but allow them in checked luggage?

The new security measures suggest a difference in the potential threat associated with carry-on luggage versus checked baggage. Checking electronic devices subjects them to a different screening process and removes them from passengers for the duration of the flight.

“The bags are screened in a different way, often using more advanced technology,” Waters said. “The policy separates the devices themselves from their owners, and they’re placing them into the cargo hold as opposed to having them potentially moving about in the cabin.”

Explosives are easier to spot in checked luggage because the screening process relies on explosive detection systems, which can be more thorough than the standard x-ray machine used at the carry-on security checkpoint, Jeffrey Price, an aviation security expert and aerospace professor at Metropolitan State University of Denver, said in an email.

Price said it’s harder for someone to detonate a bomb when it’s in cargo because that would mean setting it off with a timer or with a trigger device based on barometric pressure. “It’s less complicated to command detonate when it’s with you,” he said.

Why target these airports?

The new restrictions affect airports in Amman, Jordan; Kuwait City, Kuwait; Cairo; Istanbul; Jeddah and Riyadh, Saudi Arabia; Casablanca, Morocco; Doha, Qatar; and Dubai and Abu Dhabi in the United Arab Emirates. A statement from the Department of Homeland Security said the affected airports and airlines were selected “based on the current threat picture.” Sheldon Jacobson, a professor at the University of Illinois at Urbana-Champaign who studies aviation security, questioned whether the rules could create a “porous security environment” if other countries don’t adopt similar rules. The United Kingdom followed the U.S. on Tuesday by announcing a similar ban on certain electronic devices, affecting select flights from six countries.

Waters said the targeted rules were likely a result of the TSA’s varying confidence levels in screening procedures at different airports.

How will this affect travelers?

The primary effect on travelers will be two-fold, Waters said. They’ll have to endure a long flight without a laptop or tablet, and they’ll have to check a bag if they’re traveling with one of these devices.

Waters, who will be traveling through one of the 10 affected airports during a trip next week, praised the measures as a “very reasonable set of mitigation strategies to limit the overall risk.”

While some travelers have already criticized the rule as a hassle, Waters said he saw it as a relatively small sacrifice.

“I’m never a guy who checks a bag, and I’m always a guy who uses a laptop during the flight,” Waters said. “I will be inconvenienced by this, and I have absolutely no heartburn whatsoever with what TSA has done.”