WASHINGTON — Technology aimed at preventing the deaths of children in hot vehicles is no substitute for careful caregiving, federal officials said Monday, describing some products being sold as “unreliable.”

A study released on Monday examined products designed to stop children up to age 2 from being left in parked closed vehicles. At least 527 children — more than half of them under 2 — have died in those circumstances since 1998, according to the report, which was done jointly by the Department of Transportation, the National Highway Traffic Safety Administration and Children’s Hospital of Philadelphia.

“There should never be any notion of a single absolute perfect solution,” said David L. Strickland, administrator for the National Highway Traffic Safety Administration, warning that too much reliance on technology could potentially contribute to a false sense of security.

“While these devices are very well intended and we do appreciate the manufacturers and inventors, we have found a number of limitations in these devices,” Mr. Strickland said. “We don’t think they can be used as the only countermeasure to make sure that you don’t forget your child behind in a car.”