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Can cops search your cell phone without a warrant? The question is tying up American courts, where judges are struggling to protect personal privacy without denying police a key crime-fighting tool. Meanwhile, smartphones now contain more evidence than ever before — and it’s become easier for suspects to wipe the phone from afar in the time it takes to get a warrant.

The legal question is going to the Supreme Court. But, in the meantime, a law professor is proposing a simple, low-tech solution: when making an arrest, cops should stick the cellphones in a Faraday Bag or simply wrap the phone in aluminum foil. Doing so would give the police time to ask for a warrant to search the phone, and also prevent the suspect from wiping its contents in the meantime.

The idea is set out in a paper by Adam Gershowitz, a William and Mary Law School professor, titled, “Seizing a Cell Phone Incident to Arrest: Data Extraction Devices, Faraday Bags or Aluminum Foil as a Solution to the Warrantless Cell Phone Search Problem.”

The paper, first reported by the Wall Street Journal, discusses situations where police arrest someone and would like to search their phone for more evidence. Under the Fourth Amendment, cops can search a person’s pockets and open containers such as a briefcase, but not closed locations (unless it’s an emergency). Courts, however, disagree on whether a phone (and its contact list, call logs, pictures and so on) is like a briefcase or more like a locked container that requires special permission to search.

Gershowitz noted that some police departments are using a device called the “Universal Forensic Extraction Device,” which can suck up the entire contents of a cell phone in less than 90 seconds so investigators may examine a copy of the contents later on. He adds, however, that the devices are too expensive to provide to every single cop and, that civil liberties groups like ACLU have challenged their legality.

The more low-tech solution is to give each patrol a Faraday Bag, like the ones at right, which block wireless transmissions, and sell for as low as $10. Here’s some for sale on Google:

Or poorer police departments can simply turn to Reynolds or another aluminum foil maker:

they can simply buy a roll of aluminum foil for $2 in a grocery store and leave it in their vehicle. When the police seize a phone, they simply have to wrap the phone in a few layers of aluminum foil and the chance of remote wiping of the phone will be almost completely eliminated. [empahsi

From a technical point of view, the plan appears sound given that several layers of foil would work the same way as a Faraday Cage (of course, police might need to unwrap it inside some sort of shielded lab because, as soon as the phone re-established a signal, it might execute a data wipe.)

From a policy standpoint, the plan may also provide a sensible balance (provided police don’t start seizing phones more frequently): it promises to preserve traditional privacy rights of those arrested while also giving police a key tool to, well, foil crime.