An ordinary-looking grid map of Riyadh adorns one wall of a command-and-control center deep inside a government building in Saudi Arabia's capital.
The map is higher-tech than it appears at first glance. Tiny embedded lights flash red when certain cellphones - those belonging to suspected terrorists - initiate or receive a call. Teams of officials from Saudi Arabia, the FBI, the CIA, and the US Treasury Department decide instantly whether simply to watch and listen to the suspected terrorist - or to send in screaming police cars to nab him.
So far, officials say, this technology - and others - has enabled them to interrupt several terror plots and nab dozens of suspected terrorists. Certainly it hasn't served as a panacea, as the attacks on foreign workers in Saudi Arabia's oil-worker compounds last weekend show. At least 22 people, including one American, were killed when terrorists stormed a compound where foreign oil workers lived. One terrorist was captured, while three others escaped using hostages as shields.
It doesn't take long for terrorists to figure out how authorities are tracing them and then change methods. Still, the technology has proved helpful in rolling up cells in Europe, the Middle East, Southeast Asia, and America. "Today, gumshoe is really a lot more electronics," says Peter Crooks, a retired FBI agent who specialized in counterterrorism. "They have some pretty sophisticated equipment."
Cooperating officials in many countries have been quietly chipping away at terror cells over the past several months. Recent progress includes:
• Japan arrested five foreigners with suspected ties to Al Qaeda on May 26. Pakistan had detained four others on May 24.
• The Saudi government killed five suspected militants in the Buraida area on May 21.
• On May 6, the Philippines arrested an alleged cell leader with Jemaah Islamiyah, a Southeast Asian group tied to Al Qaeda.
• Spanish police arrested a Moroccan April 27, and said it was seeking five others for roles in the March 11 Madrid train bombings. So far, 19 have been detained for their roles in those bombings.
• South Africa deported five Al Qaeda members on April 9. Government officials there claim the moves led to the detentions of several others in Jordan.
• Jordan foiled what it called the most serious attempt yet to overthrow its government on April 9. Four terrorists were killed and three detained after they attempted to use chemical weapons and truck bombs against several government targets, including the prime minister's office and the US Embassy there.
Terrorists, of course, catch on to the new tracking procedures and seek safer ways to communicate. Osama bin Laden, for example, stopped using satellite phones because he found out - with the delivery of a guided missile - that the US was tracking his position via the satellite.
But terrorists found a new system that enabled them to use phones that were difficult, if not impossible, to track.
SIM cards, for Subscriber Identity Model, were developed to create a universal - and cheaper - cellphone system. Under the old approach, a resident from, say, Britain would be charged at a local rate when making cellphone calls in England. But if he were to travel to Germany, he would be charged long distance rates. Under the new system, he can buy a German SIM card - which contains a fingernail-sized computer chip - and make the same calls at local rates.
The information on pricing, minutes, and local telephone numbers is encoded in the chip. But since there is no need for a local record of the purchaser's name and credit information, as there is when setting up a land line or a traditional cellphone account, it makes it easier for people to use phones undetected.
"What we're seeing is that people who want to remain invisible to law enforcement are doing things like this in order to evade interceptions," says a telecommunications engineer who's helped develop ways to track cellphone users. Still, he adds, "this doesn't make you immune from interceptions."
After years of tracking terrorists, investigators have amassed a large database of land-line and traditional cellphone numbers they are watching (or listening to). All it takes is a call from one of those numbers to a phone with a SIM card to discover who's using the undetectable phone.
This is what led investigators to Khalid Sheikh Mohammed, the mastermind of the 9/11 plot, who was arrested in Pakistan in March 2003. A suspected terrorist whom German authorities were watching placed a call to someone with a cellphone in Pakistan on April 11, 2002.
No one spoke. But authorities said the call was made to alert Mr. Mohammed that an attack on German tourists visiting Tunisia was about to take place, which it did, later that day. Authorities began tracking the SIM card, which Mohammed supposedly moved from phone to phone, creating problems in locating his position.
But pinpointing the location of the phone was much easier. Investigators tracked it by analyzing the signals from different cellphone towers. The time it takes a signal to "propagate and return back tells how far the cellphone is from the tower," says an engineer. The reason the red lights flash so quickly in the Saudi command and control center is that "the timing is nearly simultaneous," he says.