WASHINGTON (Reuters) - Major automakers said on Wednesday they have agreed to equip nearly all U.S. vehicles with systems to remind motorists of passengers in the back seat, by model year 2025, in an effort to avoid deaths of young children left behind in hot cars.

FILE PHOTO: New cars are shown for sale at a dealership in National City, California, U.S., June 30, 2017. REUTERS/Mike Blake/File Photo

The announcement on so-called rear seat reminder systems comes as the U.S. Congress has been debating making it a requirement for new cars.

Lawmakers say more than 800 children in parked vehicles have died from heatstroke in the United States over the last two decades. U.S. regulators say 53 died last year, the most in two decades.

The 20 automakers taking part represent nearly 98% of all U.S. vehicle sales and committed to include audible and visual alerts on vehicles by the 2025 model year, or a year later if a redesign is involved.

The automakers include General Motors Co GM.N, Ford Motor Co F.N, Volkswagen AG VOWG_p.DE, Toyota Motor Corp 7203.T, Hyundai Motor Co 005380.KS and Honda Motor Co Ltd 7267.T.

Fiat Chrysler Automobiles NV FCHA.MI said it will eventually adopt the reminder technology on all vehicles worldwide but said timing by region will vary, while in July Hyundai said it would make the systems standard on most U.S. vehicles by 2022.

GM has had a system on some U.S. vehicles since 2016 that provides audible alert and a visual reminder on the vehicle dashboard to check for a child before exiting.

The systems generally operate to alert a driver to the presence of a child if a rear door was opened at the start of a trip. Some vehicles have ultrasonic sensors that can detect the movements of children and pets; a Hyundai system will honk the horn and send an alert to the driver’s smartphone if it detects movement.

Some safety advocates want more advanced systems that would detect the actual presence of a child in the back seat mandated.

In July, the Senate Commerce Committee approved legislation to eventually require automakers to install the technology on new vehicles.

U.S. Senator Roger Wicker, a Republican who chairs the Commerce Committee, said in an interview the voluntary agreement makes the legislation unnecessary. Under the legislation being considered, the National Highway Traffic Safety Administration (NHTSA) would be compelled to write regulations and then automakers would have at least two years’ lead time.

“This gives us essentially everything we’ve asked for and it does it sooner,” said Wicker. “It is a huge win.”

NHTSA plans to double its investment in its annual heatstroke awareness campaign “Where’s Baby” and plans to convene automakers, technology companies, child product manufacturers and others for a safety summit later this month.

NHTSA typically takes years to write regulations. For example, a proposal to require automakers to send email notifications of recalls has been pending for more than three years.

Wicker’s bill would also direct states to use a portion of highway safety program funds to educate the public on the risks of leaving a child or unattended passenger in a vehicle, and require the Transportation Department to commission a study on retrofitting existing passenger motor vehicles.

U.S. Representatives Frank Pallone and Jan Schakowsky, Democrats overseeing panels on auto issues, said in a joint statement the effort is “a big step in the right direction” but “voluntary commitments don’t necessarily result in meaningful action.”

They added Congress should “pursue legislation that requires these companies to take the necessary steps to protect children and holds the companies accountable.”