IN MOST PRISONS, sharp-eyed guards keep contraband out by doing surprise shakedowns, pat-downs and body-cavity searches, and by passing visitors and packages through metal detectors so sensitive that orthopedic implants, body piercings and even intrauterine devices can make them whoop.

But Philadelphia has a new tool to keep contraband cell phones off its cell blocks: It's a furry, four-legged 60-pounder who likes Milk Bones and squeaky tennis balls.

Bomber, a Belgian Malinois, began working in the city's six prisons in January. He's the only dog trained to sniff out forbidden phones in prisons in Pennsylvania.

Following the lead of his proficient proboscis, he has found 10 cell phones in the past three months - more than guards found all last year in the state's 26 prisons.

And that's not because Philly thugs are more cunning than inmates elsewhere at sneaking forbidden phones past security, experts say.

"I just think dogs are better at finding cell phones" than metal detectors, guard searches and other screening methods, said Sgt. William Finn, who supervises the Philadelphia Prison System's five-dog canine unit.

"Dogs have a keen sense of smell," Finn added. "A dog has more than 220 million olfactory receptors in its nose. Humans have only five million."

From shivs and shanks to cash and corrosive substances, the list of what's considered contraband in Pennsylvania prisons seems longer than a repeat offender's rap sheet.

But prison officials, from rural reformatories to federal lockups, say that contraband cell phones are a growing - and sometimes deadly - problem behind bars.

In Philadelphia last year, inmate Hakeem Bey used a throwaway cell phone to order the retaliation slaying of Chante Wright, a once-protected witness in his murder case.

A Maryland prisoner used a cell phone in a similar scheme in 2007, arranging the murder of a homicide witness.

Other inmates have used smuggled cell phones to plot escapes, continue their criminal doings, coordinate prison riots and threaten witnesses, lawmakers and others.

"A cell phone is the most dangerous weapon you can get into a prison," said Terry Bittner, director of security products for ITT Industries, a Maryland-based company that developed a system of sensors that it markets to prisons to detect cell-phone signals in the slammer.

"An inmate using a cell phone is not using a cell phone because it's cheaper than calling collect," Bittner added. "They're using it to conduct their business from the inside; it's unmonitored communication. That means the state is now giving them food, lodging and health care to continue being criminals."

Pennsylvania legislators years ago outlawed cell phones in prisons after drug kingpin Ronald Whethers used one to run his narcotics operation from a Westmoreland County prison. Most other states have similar restrictions.

But the law hasn't stopped many incarcerated thugs from breaking the ban.

Some use the age-old strategies of smuggling contraband in body cavities or bribing guards. Four prison officers at Graterford were arrested in 2007 for sneaking cell phones and drugs in to inmates.

Other jailbirds have gotten more creative.

In Sao Paulo, Brazil, inmates - assisted by accomplices outside prison - bred and raised carrier pigeons to fly out to fetch cell-phone parts. Other prisons have discovered visitors chucking cell phones over fences to incarcerated loved ones. And in Tennessee, prison officials banned peanut-butter jars after an inmate used one to hide a phone, with which he orchestrated his escape.

It's a problem that promises to worsen, experts say, as technological improvements shrink the size of cell phones and their parts, making them easier to sneak into prisons and hide.

Some cell phones now are as small as a credit card, and the memory chips inserted into them - called SIM, or subscriber-identity module, cards - are postage- stamp-sized, Bittner said. That means a single cell phone can be used by countless inmates, who can just switch out their SIM cards.

Inmates who have contraband cell phones also tend to have other contraband items, said Lt. Xavier Beaufort, of the Philadelphia Prison System.

Cell phones can be big business behind bars. Some inmates will pay $300 or more to get one, and inmates with SIM cards but no phone will pay to "rent" cell phones from cellmates, Finn said.

Finn is banking on Bomber to take a bite out of that business.

Bomber is a pioneer in his field.

Law-enforcement officials for decades have used dogs to detect drugs, cadavers, explosives and missing people, and to assist officers in other ways.

But coaching canines to detect that cell smell is a new phenomenon, said Bill Reynolds, who owns the Reynolds Canine Academy, in Northeast Philadelphia, one of only a handful of schools nationally that trains dogs in cell-phone detection.

Reynolds donated Bomber last fall to Finn's unit, which also has four dogs trained to detect drugs.

It isn't clear which parts of phones the dogs detect, but Maj. Peter Anderson, head of Maryland's K-9 operations for prisons, told the Washington Post that the animals are trained using the same techniques as those sniffing for drugs and other things. They probably take in a combination of odors from various sections, he said.

New Jersey's Department of Corrections has gone to the dogs, too. Several dogs trained in cell-phone detection began making surprise sweeps of the state's 14 prisons last October, the department said. Since then, the dogs have found 15 cell phones, five cell-phone batteries and numerous accessories, including chargers and SIM cards, corrections officials said.

Still, most prisons nationally try to quell the swell of forbidden phones by trusting technology - beefed-up front-door security, restrictive screening of jail mail and even triangulation technology that alerts guards to cell-phone signals.

And although jamming cell signals is illegal under federal law, some groups that want to use jamming technology to thwart thugs have petitioned the Federal Communications Commission to bag the jam ban.

Exactly how many cell phones make their way into prisons is unknown, because federal, state and local prison officials aren't required to keep such data. Experts say that most prison officials probably find just a fraction of them anyway.

In Pennsylvania, for example, state prison officials found just eight cell phones in 2008 (through October, the most recent month data is available), 15 in 2007 and 10 in 2006, said Susan Bensinger, a Department of Corrections spokeswoman.

Bensinger attributed the state's low numbers to aggressive screening. All visitors and staff must pass through metal detectors to get into prison and face physical pat-downs, Ben-singer said. All prison areas undergo regular, random shakedowns and searches, and officials scrutinize incoming mail, she added.

Pennsylvania is using Bittner's sensor system, called Cell Hound, in an undisclosed location, Bensinger said.

But Bittner said that metal detectors and spot searches aren't fail-safe. He suspects that thousands of cell phones are getting into American prisons every year. *

Staff writer Jason Nark contributed to this report.