An Alpharetta teen was arrested after leaving his cellphone in a car he burglarized, according to police. The teen confessed to 18 break-ins of cars, most of which were unlocked, they said.

Police said Alpharetta residents reported Sunday that cars had been broken into overnight and that items such as digital cameras and cellphones were stolen.

"We've had a large number of auto break-ins this year, due to the economy being down," Alphareta police spokesman George Gordon said.

While responding, an investigator noticed a cellphone in the car that didn't belong to the car's owner. He learned the identity of the phone's owner by calling a number on the contact list.

"He said, 'I've just found this phone. Can you tell me who it belongs to?' " Gordon said.

The name matched that of a 15-year-old who had previously been charged with theft.

Police went to his house, where the boy's mother agreed to a search, police said. The search yielded the missing items, which Gordon said were probably going to be sold.

He has been charged multiple times with entering an auto and gave police names of two accomplices. No other arrests had been made as of Thursday morning, Gordon said.

Alpharetta police have made several car break-in arrests this year, Gordon said, including that of an attorney charged with stealing $25,000 to $45,000 worth of property. Officers are patrolling business and residential areas, particularly during lunch hours. The department has even parked an unmarked car with valuable items in it to see if someone will break into it.

Said Gordon, "We continually tell citizens to not leave items of value in their vehicles."