ORLANDO, Fla.  —  When 11-year-old Jessica Lunsford was kidnapped and murdered last year, Joe Dawson immediately began gathering signatures to enact stricter penalties for registered sex offenders.

Now, Dawson is teaming up with a California-based technology firm to introduce the first cell phone that uses the Global Positioning System to alert parents when a child is walking near a sexual predator's home.

CATS Communication Inc. allows parents to build "geofences" around every listed child predator that lives within their ZIP codes.

The phone alerts parents through an e-mail, text message or pager if their child enters that zone, said the company's vice president, Jon Kudla.

Linked with the Family Watchdog's national database of registered sex offenders, the phone will update with new zones every time the a new name is added to the database.

"It's important for parents to know when their children are interacting near those people," said Kudla, a father of three.

The feature, which hits the market in the next 60 days, costs $19.99 a month for the first phone and $9.99 for each additional phone.

It's part of Cat Trax, a Sprint Nextel (S) wireless phone CATS introduced last year with capabilities to track kids with a GPS chip.

Other products, like Wherifone and Teen Arrive Alive, also help parents keep tabs on their children's whereabouts and driving habits — for example, how fast a teen is driving on the highway.

But CATS Communication is the first company to add the sexual predator component, said industry analyst Will Strauss of Forward Concepts.

Small companies using GPS systems to cater to niche markets "are coming out of the woodwork," said Strauss, allowing consumers to locate everything from Chinese restaurants to a lost Alzheimer's patient.

Dawson, who lives in Jessica's hometown of Homosassa, was ultimately successful in getting the Jessica Lunsford Act passed.