[mseebach]

An effective deployment of the device would probably involve a sort of sluice gate setup, that will detect traffic through an outer perimeter and, when triggered, seals an inner perimeter. The distance between the two is designed to be greater than that which can be covered on foot in the time the device takes to make a detection.

That, of course, ignores a central lesson of the Brussels attacks: They happened before security. This device might make it reasonably hard to get explosives into an airport building and concerts halls (because thousands theatres like the Bataclan are totally going to invest millions in these devices and the necessary physical reconstruction), but there are plenty of other buildings where large numbers of people congregate, including busy streets that will be impossible to protect like this.

Also, having a mechanism to seal your targets inside during an attack is totally never going to be abused by the bad guys (and if you evacuate on a trigger, you just need a few guys with AKs outside the exits).

That said, I'm sure there are good applications for an effective non-intrusive explosives detector (eg in making airport security smoother) -- these attacks just ain't it.

[junto]

This is exactly the key point. You either have a queue of people inside the airport, or outside waiting to go through security. The target has just been moved and is equally as accessible (perhaps more so) as before.

[mseebach]

The point is that you could deploy this device without having a queue, just a door to slam in the face of a positive detection. Worst case, you need to space people out a bit.

[junto]

Wherever you have a funnel, you get a queue. You have people standing outside waiting for the bus, smoking a cigarette. People gather and there is nothing that you can do about it.

[mseebach]

Then don't have a funnel, or have enough of them. I've never queued, except for maybe the briefest of moments, to enter an airport building, even though you always have to pass through a "funnel" (aka draft-preventing double doors[1]).

Even the narrow automatic one-way sluice doors[2] increasingly popular as you leave the secure area of an airport only ever seem to cause a queue when some idiot tries to go back, and security has to reset them.

When there's a queue at security/immigration it's because the checkpoint is understaffed (or otherwise under-provisioned), not because there's a checkpoint.

1: http://cdn.kone.com/www.kone.co.uk/Images/49562_Entrance_dou...

2: http://www.recorduk.co.uk/images/getImage?t=product&img=imag...

[GordonS]

> I've never queued, except for maybe the briefest of moments, to enter an airport building

Probably because most airports don't have security before entering. For those that do, there are indeed large queues outside. Mumbai airport is one such example.

[rbcgerard]

The logical extension of preventing terrorism before security is expanding security further and further away, until it's in your home