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.

Some of the containers in this new batch are being equipped for continuous communication; Savi is working with Qualcomm of San Diego, CA, to connect the seals with transponders that can communicate with satellite tracking systems, sending alerts in real time no matter where a container is located-on the high seas, at port, or bumping along on a truck chassis or railcar. Because continuous real-time communication is more expensive-how much more is not yet clear-the initial tests involve high-risk cargo like hazardous materials, or high-value cargo such as pharmaceuticals.

The cargo industry’s next goal is more ambitious: to introduce the world’s first “smart containers,” with multiple sensors manufactured into them. Savi is working with CIMC of Shenzen, China, the world’s largest cargo container manufacturer, to design and develop the first prototypes by the end of this year. If all goes well, these next-generation containers could be in commercial production next year.

A smart container made from scratch will do much more than detect if its main seal has been breached. For example, if an intruder tries to cut or drill through its sides, light and motion sensors inside can communicate with the seal, which can transmit a tamper alert either via the Internet or by setting off a light or sound alarm. In the future, additional sensors could detect chemicals, radiation, and the residue of explosives. Such a container would have “a mayday’ capability, in which it can recognize an unacceptable condition and report its identity, location, and condition,” says Michael Wolfe, principal of the North River Consulting Group of North Marshfield, MA, which advises government and industry on security technologies.

But even the smartest containers may still need inspections: an inspector who learns that a container has been breached might need to find out what has been placed inside. Today’s technologies, however, are inadequate for detecting the biggest threat: a nuclear bomb or radioactive “dirty bomb.”

One possible solution: a gamma ray detector with an additional imaging component that reveals the shape of the materials emitting radiation. That’s what a group led by Richard Lanza, a nuclear engineer at MIT, has prototyped. It’s an array of small detectors that collect gamma rays and produce a fine energy spectrum that gets processed into a faint image of the radiating object.

This allows inspectors to identify innocent materials that give off small amounts of radiation-like certain medical supplies or objects made from granite-without wasting time on manual inspections. Prototypes of the detectors are currently being tested at the Lawrence Livermore National Laboratory in Livermore, CA.

Deployment will depend on the outcome of these tests, but the MIT device is part of an ambitious vision for the future of nuclear-explosives detection, says Richard Wagner, a physicist at Los Alamos National Laboratory who is helping evaluate new detection technologies for the federal government. “Eventually we hope to deploy hundreds of thousands of detectors,” everywhere from seaports to highway border crossings, he says. Such a grand scheme might cost $10 billion; but the cost of detecting a nuclear bomb, clearly, is much cheaper than the cost of letting one through.