On Tuesday morning, the Department of Homeland Security announced new restrictions for personal electronics on direct flights to the U.S. from 10 airports in the Middle East and North Africa. Devices larger than a cellphone will not be allowed in the cabin, though they will be allowed in checked baggage.

Later Tuesday, the U.K. announced it would be enforcing a similar rule — using a slightly different list of countries.

The rule change in both countries was unexpected and the explanations for it cryptic.

Here's a quick look at what we know, and what we don't.

We know the U.S. restrictions are motivated by concern about terrorism ...

The Department of Homeland Security says: "Evaluated intelligence indicates that terrorist groups continue to target commercial aviation and are aggressively pursuing innovative methods to undertake their attacks, to include smuggling explosive devices in various consumer items."

... but why now? Is there new intelligence, or new analysis? Is there a specific threat?

DHS has been tight-lipped about its motivations for the change.

"It simply has to be based on some specific intelligence," security expert Bruce Schneier told NPR by email. "It's too focused on a particular tactic to be anything else."

But DHS wouldn't confirm any specific threat or say whether it is drawing on newly discovered intelligence or a new analysis of existing intel; instead, it simply refers to "ongoing," "longstanding" and "continue[d]" threats.

Given deep rivalries between Middle Eastern and U.S. carriers, some analysts have implied or outright alleged business interests are at play as well. The DHS restrictions will inconvenience some passengers but not hurt U.S. carriers, since they don't use those airports.

That logic doesn't explain the U.K. rule, however, which affects both foreign carriers and British companies, including British Airways and EasyJet.

We know the countries affected ...

There are 10 specific airports covered by the U.S. policy, located in eight countries:

Worth noting: This list of majority-Muslim countries has no overlap with the list in President Trump's much-discussed travel ban. The countries affected by the electronics policy are generally wealthier, generally stable and all traditional U.S. allies, NPR's Greg Myre says.

The U.K. version of the rule has a differentlist of countries, which omits Qatar, Kuwait, UAE and Morocco. (It also adds Tunisia and Lebanon, which don't have direct flights to the U.S., according to .)

... but why those countries?

The choice of affected flights to the U.S. is based on "evaluated intelligence" that "the threat exists at the 10 last point of departure airports," DHS says. That's why it doesn't cover flights tothose countries, or flights from those countries with a connection elsewhere.

But, again, officials have offered no details on that intelligence or that "threat," and there's no indication of why the U.K. would have a different list.

The focus on individual airports could suggest possible concerns over screening or security procedures — security at the Cairo airport has come under scrutiny before, for instance. But the list also includes the Abu Dhabi airport, which is one of relatively few airports where U.S. Customs officials are stationed abroad to conduct pre-clearance inspections.

And DHS, again, offered no details about any such concerns.

We know the rule focuses on electronics ...

Specifically, devices larger than smartphones — like laptops, tablets, e-readers, cameras, portable DVD players, "electronic game units" and travel printers or scanners.

Medical devices will be allowed in cabins, after extra screening.

(A quick note: The U.S. rule doesn't specify how big a "smartphone" is. DHS seems to have little patience for the question, saying the size of a smartphone is "well understood by most passengers." The Brits are more helpful, defining a normal-size smartphone as no bigger than 16 cm x 9.3 cm x 1.5 cm [6.3 inches x 3.7 inches x 0.6 inches])

... but why electronic devices, specifically?

You probably remember some previous airport security changes inspired by specific threats. The "shoe bomber" tried to set off a bomb, and passengers had to take off their shoes; authorities uncovered a plot to use liquid explosives, and the TSA banned liquids in carry-ons.

It's not clear what may have inspired the change announced Tuesday. The agency does point to two recent attacks on airplanes — but only one involved a laptop packed with explosives. That failed attack, in Somalia, happened more than a year ago at an airport with no flights to the U.S.

The other was the deadly downing of a Russian passenger jet over Egypt in 2015. ISIS claimed to have carried out that attack with a bomb inside a soda can, which some analysts call plausible. DHS noted the incident in a Q&A Tuesday but didn't suggest consumer electronics were involved.

We know the rule puts most electronics in the cargo hold ...

Checking the devices means they'll still be on the plane, just in a different location.

Of course, this will frustrate some passengers. It's not just a question of having the devices handy for a lengthy flight. There's also the risk of expensive electronics being broken, lost or stolen while out of the passenger's control.

... so what exactly does that achieve?

Analysts have a mixed view on what this policy — phones allowed in the cabin, other devices in the hold — would actually do.

Nicholas Weaver, a computer scientist at the University of California, Berkeley, told The Guardianit was a "weird" way to promote security.

"If you assume the attacker is interested in turning a laptop into a bomb, it would work just as well in the cargo hold," he told the British newspaper. "If you're worried about hacking, a cellphone is a computer."

Others note that while a bomb in the cargo hold canbring down a plane, it's more challenging.

"Forcing it in the plane's hold would make it much harder to detonate, since the terrorist has to design an automatic mechanism rather than doing it manually," Schneier told NPR. "Remember the crude techniques by the shoe and underwear bombers?"

And if a bomb does go off, Wiredreports that the cargo hold is a safer place — relatively speaking — for that to happen.

Alternatively, moving electronics into checked baggage might allow more intense screening of the devices, as The Atlantic notes.

At the risk of being repetitive: DHS has offered no details on what its rule is meant to prevent or ensure.

And finally, we know the rule is going into effect soon ...

DHS says airlines have 96 hours to put it into effect, as of Tuesday's 6 a.m. ET announcement.

White House press secretary Sean Spicer, asked for the reason for the delayed implementation, said you need to give airlines an "opportunity to get those procedures in place."

"I will tell you that implementing something of this nature in that time frame is pretty darn quick," he said.

... but how long will it be in place?

It's not clear. DHS says the limits will be in place "until the threat changes."

DHS and TSA "continue to evaluate our aviation security processes and policies," the department says, and "as threats change, so too will TSA's security requirements."

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