"A handful of these knuckle heads will try to bring something in here, and that's what we're after," said Chief Warden Doug Weber.

Tobacco has been outlawed in state prisons since 2000. Cell phones aren't allowed because prisoners can use them to threaten people, plan escapes or cause other trouble.

The dogs — Sadie and Toby — sniffed out a can of chewing tobacco, a pack of cigarettes and two cell phones during a demonstration Wednesday. But they passed on a television, CD player, landline phone, remote control and stereo.

When they picked up the scent, the Labradors — known for their hunting skills — froze.

K-9 Sgt. Mark Kannenberg, Sadie's handler, said inmates were initially skeptical that a dog could sniff out such a specific item: "They had the same reaction I did — you're lying," he said.

But he said the dogs can distinguish between cell phones and other electronics because the phones have a unique odor.

Just one phone has been found in the maximum security area of the South Dakota State Penitentiary, and that was linked to an employee who was fired, Weber said. People entering that part of the prison undergo shakedowns and strip searches, and all items are scanned.

Most of the confiscated cell phones have been found in minimum-security areas, Weber said.

Weber said normal phone calls from the prison are recorded, so prisoners can't get away with much.

Most tobacco comes in through visitor areas. Inmates often smuggle it in by hiding it in a body cavity or swallowing it and regurgitating it later, Weber said.

The dogs are based at the state penitentiary in Sioux Falls and the minimum-security prison in Springfield, but they also patrol prison property in Rapid City, Pierre and Yankton.

Maryland and Virginia were the first to train dogs to find cell phones, which have caused problems in several prisons.

In Texas, a death row inmate and two relatives were indicted last month in an alleged cell phone smuggling case that led to a statewide prison lock down.

In Kansas, convicted killer John Manard planned his 2006 prison escape using a cell phone smuggled in by an accomplice. The following year, two inmates escaped another Kansas prison with the help of a former guard and a smuggled cell phone.

Mark Robertson, owner of Positive Response Canines of Jackson, Tenn., said more agencies are calling for his training services because of the growing problem.

"You've got inmates with nothing to do but time to think of crimes to commit," he said. "And there's no way to track their phone calls because these are phones that aren't registered to them."