We're taking some additional specific steps. In light of the nature of the liquid explosive devices which were designed by the plotters, we are temporarily banning all liquids as carry-ons in aircraft cabins. That means no liquids or gels will be allowed in carry-on baggage. Any liquids or gels have to be checked as part of baggage to go into the hold. There will be exceptions for baby formula and medicines, but travelers must be prepared to present these items for inspection at the checkpoint, and that will allow us to take a look at them and make sure that they're safe to fly. We are taking the step of preventing liquids from getting into the cabin to give us time to make adjustments in our current screening tactics, based upon what we learned from this investigation concerning the nature of the devices that these individuals were constructing.

This is temporary, folks ... Temporary. (Think Iraq War.)

These changes sound complicated, but it is very, very simple. The major change is that passengers are no longer allowed to bring liquids through the checkpoint and onto the plane.

That is the big change. Other than that, it is getting used to the new process, and we're very confident that as time goes on that will occur.

Hrm. That doesn't sound so temporary.

Beverly?

Q Mr. Secretary, there's so much emphasis here on liquids. Was the fear that they were planning actually to assemble a bomb on board the aircraft by mixing liquids?

CHERTOFF: I would say certainly one of the considerations or one of the concerns we had is the possibility of bringing on board a number of different components of a bomb that -- each one of which would be benign but when mixed together would create a bomb. And as we assess exactly what the design of these devices was or the planned design was, I think it'll give us a better ability to tailor our countermeasures in order to pick up what appears to be a quite sophisticated conception of how to execute a terrorist bombing plot.

...

Obviously, we're always assessing and examining the challenge posed by different kinds of improvised explosive devices. We do use various kinds of techniques for different kinds of bomb-making. But when we do see a sophisticated design, we want to make sure that we properly engineer our countermeasures to be able to detect it. And so while we're in the process of assessing that -- and, you know, honestly, some of these are pretty difficult -- we want to, frankly, take the most protective stance. And that's why we have, for the time being, excluded liquids from the cabin.

Sounds like this is semi-permanent until devices capable of detecting the suspect chemicals have been installed at all domestic airports. Then this rule will only apply to international flights. But I suspect this is a long-term rule change for international flights.

Homeland Security Chief's News Conference