Proponents say the states' measures will overhaul outdated digital privacy laws and help increase oversight of specific surveillance tools that law enforcement agencies have been using that critics say mirrors federal surveillance technology.
The bills taking shape in at least 14 states include a Colorado proposal that would limit the retention of images from license plate readers, an Oregon bill that would require "urgent circumstances" to obtain mobile phone location data and a Delaware plan that increases privacy protections for text messages.
Supporters say the measures are needed because technology has grown to the point that police can digitally track someone's every move. "We need to stand up and protect our liberty," said Republican Missouri state Sen. Rob Schaaf, author of a digital privacy bill. Police groups, however, say the moves will in some cases hinder efforts to deter or solve crimes. "It would cripple law enforcement's ability to do investigations," said Bart Johnson, executive director of the International Association of Chiefs of Police.