Bomb Threat Posed by Pants, Belts

This article describes the ways of smuggling bombs by terrorists onto aeroplanes. There is still little technology to prevent terrorists from smuggling plastic or liquid explosives.
Nowadays,

"there are more than 100 types of explosives"

said James O'Bryon, an aviation security consultant.
The reason why it is easy to bring the explosives onto planes is because metal detectors are designed to detect weapons, not explosives. Another problem is that security can't use X-ray detectors because radiation is unhealthy for people.
Recently, terrorists have planned to use a combination of acetone and hydrogen peroxide to create a high explosive.

"The chemicals could be mixed on board (...) and then detonated using a spark generated by a battery-powered device like iPod or cell phone (...). Or the ingredients might have blown up when mixed without an electric detonator."

The similar situation is with plastic, that could look like, for example, sandwich to a screener.

"At some airports, passengers must pass through "trace portal" chambers where puffs of air knock off molecules that are instantly tested for telltale particles left over from bomb-making."

If such a machine is not programmed to detect specific materials, then it misses it.
...and there are only six machines in U.S. airports.

"Ideally, new technology would analyze baggage in several different ways at once, looking at everything from density and chemical makeup to atomic number analysis"