GPS tracking of released sex offenders is increasingly popular nationwide, but a pilot project here ran into a unique problem: Washington's geography.

In 2003, legislators gave the state Department of Corrections $100,000 to put 40 Level 3 sex offenders — those considered most likely to re-offend — on so-called "passive" Global Positioning System monitoring.

The technology requires uninterrupted cellphone service to track offenders' movement using satellites. But in Western Washington, tracking was interrupted by rugged terrain and skyscrapers and by sparse cellphone coverage in Eastern Washington.

In all, the GPS devices recorded nearly 4,000 "notices of violation," most of them because of technical problems, said Lin Miller, the project manager.

He tested a device on himself but his signal was lost when he was among downtown Seattle buildings and in a snowstorm near Olympia.

Earlier this year, the state of Florida spent $3.9 million to put 1,200 released sex offenders on GPS tracking.

But a key contractor suddenly quit without explanation earlier this month after two weeks of testing.

The passive GPS technology tested in Washington does not provide real-time monitoring. Instead, it sends coordinates only after the paperback-book-size GPS device worn by the offenders is put in a docking port and its data uploaded to DOC computers.

Real-time tracking — called "active" GPS — requires too much staffing to be feasible, said Miller.

Even the passive version is labor-intensive: The pilot project found caseloads must be no more than 25 offenders per officer to allow each violation to be investigated.

"People need to know it is not a technology that prevents crime," said Miller. "It's not having a parole officer in the back pocket."

Staff researcher David Turim contributed to this report.