Do you ever get the feeling you're being watched? Walking down the street, do you sense that someone somewhere is keeping an eye on you? These days, chances are, you're right.

A growing number of cities across the United States and abroad have installed networks of closed-circuit television (CCTV) cameras. Police monitor the video in an effort to prevent crime and catch lawbreakers in the act. You've probably seen the cameras; they're intentionally made conspicuous. Signs let you know your actions are being recorded.

This law enforcement trend started in the United Kingdom in 1986 with three cameras in a 1-square-mile area in a town called King's Lynn [source: Nieto]. Today, England has more CCTV cameras than any country in the world, with half a million making up its network, nicknamed the "Ring of Steel" [source: Nieto]. Many U.S. cities, including New York, Philadelphia and Chicago, followed suit and began installing the police surveillance cameras in the early 1990s. Even the Jewish Holy Land in Jerusalem is wired with CCTV systems [source: National Institute of Justice].

These systems transmit live signals to television monitors at police stations. The cameras are similar to the ones commonly found in convenience stores and banks, which police and security departments have used for decades to solve crimes. CCTV systems sales jumped by almost 700 percent from 1980 to 2000 [source: National Institute of Justice]. As you can imagine, crime cameras don't come cheap. In fact, Great Britain's Ring of Steel cost more than $330 million from 1999 to 2001 [source: Welsh and Farrington].

­With all the money being pumped into these mechanized eyes, you might wonder how well they curb crime. That depends on who you ask. Law enforcement officials generally support them, citing significant drops in violent crime. On the other hand, comprehensive studies by the American and British governments have shown otherwise.

Why do these reports of effectiveness vary so much, and who's right? Read on to find out the answers, along with why some Americans feel the cameras violate the Constitution.