The cargo container-that ubiquitous truck-sized box that carries goods around the world-could be the ultimate poor man's missile. Each year more than 48 million loaded cargo containers move between the world's seaports. But of the six million that arrive in the U.S., only 5 percent have their contents visually inspected or x-rayed, opening the possibility that terrorists could use them to smuggle in nuclear material, explosives, or even themselves. Many of the world's ports are joining a U.S.-led effort to manually inspect containers considered high risk; but at the same time, a host of technologies are being readied to plug this security hole.

It's a big job that starts with small electronic seals. This spring, Savi Technology of Sunnyvale, CA, and 65 technology companies and shipping industry partners concluded the first test of a new class of electronic seals that both track containers and detect intrusions. Affixed to a container's main latch, the seal has two functions. First, it serves as a radio frequency identification tag, allowing a container's movements to be recorded automatically when it passes tag readers on loading cranes and port gates or in distribution facilities. That's a technology already common in military containers, and it was recently used during the Iraq war.

But the new seals go a step farther, detecting break-ins. Opening the container breaks a magnetic field surrounding the seal; this event, and the time it took place, are recorded on a memory chip. The next time a breached container passes a tag reader, an intrusion alarm is automatically triggered, flagging the container for inspection.

The test was successful enough that several thousand seals have already been deployed to various government agencies and major shippers. According to Lani Fritts, a vice president of business development for Savi, the same consortium of 65 companies has now begun a second global field test that will ultimately involve 5,000 containers fitted with the electronic seals. What's more, the infrastructure being set up by the consortium will communicate automatically with government agencies like U.S. Customs and Border Protection.