With the press of a button, Matt Peak can do something the makers of his Chrysler Pacifica minivan never intended: take his hands off the steering wheel while he is driving.
The retired aircraft mechanic then sits back and observes while the car cruises at 55 miles an hour past subdivisions and a golf course near his home in Brighton, Mich.
"Scary as heck, the first time you do it," Peak said, resting his hands on his knees during the drive with a Wall Street Journal reporter. But now it is part of his everyday routine.
Peak's hands-free experience, enabled by an aftermarket device from a company called Comma.ai, cost him $1,000 and required about an hour to set up. The company says the device works on more than 350 vehicle models dating back to 2014.
But some drivers have fallen asleep or slammed into stopped vehicles while using the device, according to police and incident reports viewed by the Journal. At least five crashes, including three deaths and 14 injuries, have been linked to Comma.ai, according to the National Highway Traffic Safety Administration, or NHTSA. The regulator opened an investigation into the device in September.
The device is testing the frontiers of technology that automakers increasingly see as a lucrative subscription business. Driving-assistance technology spans a range of capabilities, from lane-assist to adaptive cruise control to supervised hands-free driving. No car company offers fully autonomous technology; even Tesla's Full Self-Driving is described as requiring human supervision.
Comma.ai's device enables functions that most automakers don't, or can't, offer themselves. Exceptions include Tesla's FSD, a $99 monthly feature that allows hands-free driving and point-to-point navigation. General Motors and Ford's Super Cruise and BlueCruise allow for hands-off driving on certain highways.
Comma.ai's device is legal, highlighting what experts say are gray areas around automated driving-assistance technologies, or ADAS. There are no federal safety standards for this technology. NHTSA has had its hands full investigating the safety of automaker-designed systems, said Michael Brooks, executive director of the Center for Auto Safety, a Washington, D.C., nonprofit.
"The agency is struggling to keep up with advanced driver tech, and this is another area that deserves more scrutiny," he said.
Comma.ai said that it offers "one of the most mature driver-assistance systems available," with its users having logged more than 400 million miles collectively to date, and that its system adds driver-monitoring features that most cars lack. The company also noted that its software is free, so drivers only pay for the hardware kit for their vehicle.
"We don't believe in hiding features, especially safety features, behind subscriptions or as an upsell," Comma.ai Chief Product Officer Adeeb Shihadeh said.
NHTSA said it doesn't comment on open investigations. The agency said drivers are fully responsible for operating a vehicle and must remain attentive when using a partially automated system. About 30,000 cars have Comma.ai equipment installed.
Comma.ai is by far the leading player in such DIY self-driving kits, but not the only one. Epilog, a San Francisco artificial-intelligence company, makes a similar device called SideCar that it said works on more than 300 vehicles. Epilog didn't respond to a request for comment.
In vehicles equipped with adaptive cruise control and lane-keeping capabilities, third-party devices like Comma.ai's work by taking control of the steering, braking and powertrain functions. They essentially mimic the language in which the car's hardware communicates, said Florian Frischmuth, vice president of digital engineering at software consulting firm Envorso.
Comma.ai released its latest kit, Comma Four, last November. The device includes an inward-facing camera that tracks the driver's eyes and head position and issues alerts if it detects inattention.
Comma.ai has been selling the kits since 2020, though regulators had scrutinized the company's plans even earlier. The startup, founded by coder George Hotz, planned a decade ago to sell hardware and software that would allow car owners to install semiautonomous driving aids on some vehicles. It abandoned the effort after regulators began asking questions about the product's safety and opted to release the software behind it for free.
Automakers say consumers are free to modify cars at their own risk, and Comma.ai's device might void their warranty. Comma.ai said federal law requires automakers to honor warranties unless they can show that a particular fault was caused by the aftermarket device.
Some experts expect car companies to take steps to block aftermarket systems like this one in future vehicles. But blocking a device like Comma.ai's isn't possible for most cars on the road today, Frischmuth said. Those vehicles can't detect when a third-party system has taken control.
"It was basically a door with no lock," he said. "Anybody could walk right through."
NHTSA started receiving reports last fall of crashes involving vehicles equipped with Comma.ai's device, records show. NHTSA said preliminary data reviewed by the agency "suggests that the Comma system may not have adequately detected or responded to the in-lane vehicles."
In one 2025 case, a man named Allen Robberson slammed a used Honda Accord into the back of another car at a red light in Missouri. Robberson's car was going 80 mph and had a Comma.ai device enabled.
The crash left one occupant in the stopped vehicle with severe injuries, according to a lawsuit.
Robberson referred a request for comment to an attorney, who declined to comment. He was later charged with a misdemeanor. After the crash, according to a police report viewed by the Journal, he told first responders that "he had set the vehicle's automation to allow him to sleep."
Comma.ai declined to comment on the accident or the government probe, but stressed that its system never obviates the driver's role.
"Nothing for sale today is a self-driving car (despite any names to the contrary), and no driver should treat one like it is," a Comma.ai spokesperson said.