LOS ANGELES, Sept. 8 (Xinhua) -- Police in San Francisco are battling crimes digitally with a new genre of cell phone forensic extraction devices, it was reported on Monday.

    These devices, made by companies including Cellebrite, Data Pilot and Oxygen Software, often can extract text messages, pictures or contact lists that the phone owner thinks they have erased, so long as new data hasn't been written over the old location in the cell phone's memory, according to the San Francisco Chronicle.

    The device has become the delight of cops, the bane of bad guys and a cloud over civil liberties, the paper said.

    Since cell phone extraction devices became available in the past couple of years, they have quickly become vital tools in solving crimes, Robert Morgester, a California deputy attorney general and expert on the topic, said.

    The law enforcement version of the cell phone extraction devices differs from the commercial technology in one important regard -- the police device can only read data and cannot write back to the cell phone, in order to protect the integrity of evidence, according to the paper.

    "The reason why the cell phone is important is that you are carrying around a personal diary of who you talk to and often what you talked about," Morgester said in reference not to conversations but rather to texting, adding "Youth today communicate through MySpace and texting."

    Cell phone forensic extraction is a relatively new technology that grew out of a problem faced by consumers who switch cell phone carriers and want to port their old data to their new device, said Adi Ofrat, chief executive of Cellebrite, which has offices in Israel and New Jersey, one of the vendors the San Francisco Police Department uses.

    Since 2000, his 70-person company has sold more than 50,000 office-based cell phone data conversion systems to mobile phone carriers worldwide, he told the paper.

    But attorney Kevin Bankston with the Electronic Frontier Foundation in San Francisco said the ease-of-use and portability of forensic cell phone devices has started to chip away at the constitutional protections against searches without a warrant.

    Jim Dempsey, a civil libertarian with the Center for Democracy and Technology, explained that officers can search a suspect and his or her property, such as a backpack, at the time of arrest. But he said this was meant to discover things like weapons that could harm the officer, while extracting data from a cell phone should generally be done later, after the phone is seized but not before a search warrant is issued.