(Image: file photo via CBSNews.com)

Security cameras on the NJ Transit aren't just watching what you do, they're also listening to everything you say.

The state's metropolitan light rail system records what passengers are saying, which officials say is part of an upgraded safety plan to deter crime. Although video surveillance cameras are widely used on many transportation systems, New Jersey is pushing further with audio coverage.

But Jeanne LoCicero, director of ACLU's New Jersey branch, told sister-site CBS New York that the move is a "monumental invasion of privacy."

"We also don't know how long they keep recordings or what they are doing with them," said LoCicero, adding that there is no "legitimate reason to be recording these conversations."

First reported by NJ.com, new notices were put up saying "onboard video and audio recording systems" were in use on the trains earlier this month, but it's thought the audio collection may have started as early as last year.

But questions remain over the efficacy of the system, the amount of money spent, and privacy concerns.

The move to step up installing surveillance equipment was said to be in response to a 5 percent rise in crime on the light rail system -- an increase of seven crimes from 123 crimes reported in 2014 on the light rail system to 130 crimes reported in 2015.

How effective the audio and video surveillance system is in deterring criminals remains to be seen.

Jim Smith, a spokesperson for NJ Transit, declined to tell the New Jersey news daily how many successful prosecutions it had brought based on evidence collected from its surveillance systems.

It's also not clear exactly who has access to the data collected data. The systems are used by the New Jersey Transit Police Department (NJTPD), but it's not clear if a warrant is required to access any audio or video.

Smith also declined to comment on how long data is retained by the system, or if there are any redress mechanisms for those who audio or video was collected.

All we do know is the cost. According to the report, the surveillance equipment cost $750,000 to install on the River Line, with a $1.9 million federal Homeland Security grant going towards the eventual installation on the Hudson-Bergen and Newark lines.

Neighboring state New York sparked concern in 2014 when hidden surveillance cameras were spotted on the New York City subway, which was dubbed "deceptive" by privacy advocates.

Smith did not respond to our questions by email.