There's something inside St. Paul's new recycling bins that residents may not have realized: a tracking chip.

While the chip has proven controversial elsewhere, St. Paul says it isn't using it to monitor recycling. Still, civil liberty advocates have concerns.

The tiny electronic chips, known as RFID or radio frequency identification, allow recycling equipment to scan and identify the cart by passing a detector nearby.

Workers were already scanning them even as they distributed the carts around town. "They're basically scanning the serial number and connecting with the longitude-latitude point of the address," said Kris Hageman, environmental coordinator for St. Paul Public Works.

That'll make it easier to make sure everyone has the new bins, Hageman said, and keep track of the city's cart inventory.

But there's more to the story.

In other cities, trucks used to pick up and empty trash and recycling bins have been equipped with RFID sensors that can be used to monitor compliance with recycling requirements.

St. Paul mandates recycling, although it isn't strictly enforced. (Minneapolis officials say they don't use RFID technology in their recycling containers.)

But in Cleveland, the city instituted a $100 fine for residents who don't recycle, including folks who repeatedly fail to put their recycling out.

Some waste haulers, like one in LaCrosse, Wis., have tested video recording to monitor the stream of waste and recycling as it's collected.

St. Paul's new trucks will also have video monitors to watch recycling bins as they're emptied.

Workers from Strategic Cart Services unloaded and assembled recycling carts in an alley in the Macalester-Groveland neighborhood on Nov. 30, 2016. They were a few of about 80,000 carts distrubted by the city of St. Paul as part of its new recycling program. Tim Nelson | MPR News

That's got civil liberties advocates asking whether the carts could effectively be a new surveillance technology parked behind people's homes.

The American Civil Liberties Union has raised questions about the practice of putting tracking devices in recycling containers.

"We've heard some stories from other locations across the United States where you're actually able to inspect the contents of bins to figure out what type of garbage or recycling people have and whether they are or are not following certain recycling rules," said Ben Feist, the ACLU's Minnesota legislative director.

City officials say their contract with Eureka Recycling, which runs the program, doesn't include such inspection and there are no plans to add an enforcement mechanism to the system.

That would take a city ordinance and plenty of notice to residents to enact, said Anne Hunt, St. Paul's environmental policy director.

St. Paul policymakers weighed the use of the technology and decided it was the responsible thing to do, Hunt said.

"The city spent $3.8 million of taxpayers' money. It's 80,000 carts throughout the city. We need to keep track of the inventory and our assets," she said. "So we need to know if the cart is in the right location, if it was damaged, if it was stolen."

She also said people have an option if they're truly worried about the technology: Eureka has a drop-off site in the city's North End, where residents can take their sorted recycling and put it in giant containers themselves — no radio chips involved.

St. Paul has been doling out the blue 64-gallon bins around town over the past few months in hopes they'll boost recycling efforts.

The new bins have a greater capacity, plus lids and wheels. Hunt said the new bins will make recycling easier and more convenient.

"The old blue bins were bulky and awkward," she said. "If they were overflowing, lots of times people just throw the material in the trash."

Minnesota Pollution Control Agency officials say it'll be one of the most ambitious recycling programs in the state, because it's so big and runs weekly.