Retired Chicago Police First Deputy Anthony Riccio says the readers are a very effective tool for police.
"It alerts an officer who is in a vehicle that a vehicle is wanted or if a vehicle has been stolen and really allows an immediate follow up by officers," Riccio said.
Riccio says they have helped track down vehicles used in robberies, shootings and sexual assaults. There are now hundreds of license plate readers on Chicago highways, and more are being installed throughout the state.
"What these do is they hoover up everyone who drives past the cameras and collects that information and stores it into a national data base," said Reilly Stephens with the Liberty Justice Center.
On behalf of two Chicago residents, the Liberty Justice Center has filed a lawsuit against Illinois State Police and the state's governor and attorney general. The legal action argues that the surveillance and data collection constitutes an unreasonable search in violation of the 4th Amendment.
"All of that data is aggregated to, basically, track your movement, just in case they suspect you of something," Stephens said.
Calling it dragnet surveillance, the Liberty Justice Center says if law enforcement wants to use license plate readers constitutionally, a warrant should be required.
Riccio says the data collected from the cameras are deleted after a short period of time.
"It's only retained for a short period of time, and it's only accessed by detectives conducting follow-up investigations or officers who are alerted," Riccio said.
ISP and the offices of the governor and the attorney general did not have a response to the lawsuit.
The Liberty Justice Center plans to file similar lawsuits in others states that use the technology.