In prison, the cellphone is a deadly weapon: Inmates can use contraband phones to plot more crime, intimidate or kill witnesses or plan escape. But the introduction of the Safe Prisons Communications Act of 2009 -- which would amend federal law to allow jamming technology to block smuggled cell phones -- has prompted a showdown between jamming advocates and wireless communications companies.<p>Jammers, however, are not the only tool for battling contraband cellphones. Several companies are marketing cellphone detection as a smarter alternative to jamming. The principle is straightforward: instead of blocking signals, prison authorities can use a network of sensors to detect cellphone transmissions, measure their use and triangulate their location.<p>I spoke recently to Terry Bittner of ITT Corporation, which markets a system called Cell Hound. It's currently installed in some state and federal institutions. According to Bittner, a system like Cell Hound is more of an intel tool. Illicit phones are often hidden with other contraband -- and detectors can not only locate phones, but track the patterns of the callers. "You need to study the habit of the phone -- who uses it most of the time, how it got in there," he said. "They will never store the phone in a cell where they use it. They rent it out to other inmates. In some cases they won't use the phone." Cell Hound scans for the most common cellphone radio-frequency signatures in North America; a central server then maps the location and gives a visual alert on a corrections officer's workstation.<p>ITT is not the only company in this game, however. Israeli prisons also have a major issue with contraband phones (pictured here); Israeli electronic warfare firm Netline also markets a cellphone detection system with a central control. Cellphone detection could potentially have other applications, too: Detecting illicit cellphone use inside secure conference facilities, or to aid a network in pushing marketing messages or alerts to mobile phones.<p>Typically, law enforcement and intelligence agencies don't like to advertise what kinds of tools they use to counter or detect illicit communications. ITT, for instance, initially marketed Cell Hound in a very low-key fashion; but pending legislation in Congress, as Bittner described it, forced the company to "come out of the closet" with its technology.