California state Sen. Mark Leno (D) introduced legislation on Tuesday that would prohibit law enforcement agencies in the state from using a person’s cell phone to track their movement, unless they first got a warrant.

“Our modern day smart phones and gadgets make it easy to get directions to just about anywhere, but they also track our every move and the people we connect with in our daily lives,” Leno said.

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“Unfortunately, California’s privacy laws have not kept up with the electronic age, and government agencies are frequently accessing this sensitive information without adequate oversight,” he added. “SB 1434 carefully balances privacy concerns to safeguard Californians against improper government intrusion while ensuring that law enforcement officials can still use this technology when it is needed to protect public safety.”

The U.S. Supreme Court recently ruled that police must obtain a warrant before using a GPS device to track a suspect.

However, law enforcement agencies can obtain cell phone records from service providers, giving them access to the phone’s locational data. In addition, computers scientists have found it is relatively easy and inexpensive to set up a device to track a cell phone’s position, without any collaboration with cell phone service providers.

According to an investigation by the ACLU, cell phone tracking is widespread. While some police departments obtain a warrant to track cell phones, many do not.

“Police are taking advantage of outdated privacy laws to use our mobile phones as tracking devices,” said Nicole Ozer, technology and civil liberties policy director for the ACLU of Northern California. “Our mobile phones should be working for us, not the police. It’s time to update California privacy law so it matches our modern mobile world and keeps our personal information safe from misuse.”

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Leno’s bill would also limit search warrants for cell phone tracking to a timeframe no longer than 30 days.