The ruling failed, however, to address whether warrants must also be obtained to track suspects by using cellphone tower data and other geo-location tracking systems.

The California legislation comes as privacy groups say that numerous law enforcement agencies around the country use warrantless cellphone tracking to follow suspects in criminal cases.

Earlier this year the ACLU obtained more than from some 200 local law enforcement departments detailing their cell phone tracking practices.

All but 10 of the departments studied were found to have tracked cell phones, some of then quite frequently. Many of the departments said they obtained tracking data from phone companies without obtaining a warrant, the ACLU said.

A handful of the departments did obtain warrants though the legal standards used to obtain them varied widely, according to the ACLU.