But privacy experts and many borrowers who have the devices in their cars say there is great potential for abuse, particularly because the devices fall outside traditional state and federal lending laws.

Some find it unsettling that the technology gives lenders so much control over borrowers — particularly poor borrowers, who typically have no choice but to accept the device if they want a loan to buy a car.

“They don’t need to know what we are doing — when we go out to eat, when we go on vacation,” said Elias Sanchez, a forklift operator in Austin, Tex. “We want our privacy.” His auto dealer didn’t tell him that a GPS tracking device had been installed in his 2005 Ford S.U.V., he said.

A 2014 investigation by The New York Times highlighted the tracking technology. In a front-page article, the head of collections at a Louisiana credit union said he could monitor a vehicle’s whereabouts on his smartphone and once disabled a borrower’s ignition while shopping at a Walmart.

A mother in Las Vegas described in the article how she had been unable to get her feverish child to a hospital because her car had been shut off for a missed payment. Other borrowers have complained in interviews of being stranded, marooned in dangerous neighborhoods and cut off from their cars when they needed it the most. In Nevada, one woman testified to the Legislature that her car had been shut down on a freeway.

Some state lawmakers have taken note. The New Jersey Legislature is working to revise a bill, vetoed this month by Gov. Chris Christie, that would strengthen the disclosure requirements and add consumer protections to the devices. Under the bill, consumers would get written disclosures that a device had been installed in their car and at least 72 hours’ notice before the ignition was disabled.

The Federal Trade Commission has brought several regulatory actions against businesses in recent years over privacy violations.