WHITTIER (CBSLA.com) — The parents of a special-needs student who died after being left on a school bus in Whittier on a hot summer day thanked Gov. Jerry Brown on Wednesday for signing legislation that requires school buses to have an alarm system to ensure students are not left behind.

“Although we tragically lost our son Paul last year after he was left behind on a school bus for seven hours, we know that the signing of this bill is a warm hug from heaven that will enable all children who ride a school bus to arrive at their destination safely,” said Eun Ha Lee, mother of Hun Joon “Paul” Lee.

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The 19-year-old with autism died after being left on a bus for nine hours in 90-degree heat Sept. 11, 2015.

Senate Bill 1072 or the Paul Lee School Bus Safety Law, authored by Sen. Tony Mendoza, D-Artesia, will require school buses in California to be equipped with child-safety alarms beginning 2018.

The alarm system triggers a loud sound when the bus is turned off. The driver must walk to the back of the bus to turn off the alarm, and at the same time check to make sure no students are still on board.

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“The Paul Lee School Bus Safety Law will protect every child who rides a school bus to and from school every day,” Mendoza said. “No parent should fear that their child will not return home safely at the end of the day.”

“We failed to protect Paul. Paul, I love you. I miss you. I’m so proud of you. See you in heaven,” Paul’s mom said.

The driver, Armando Abel Ramirez, who failed to check the bus after dropping off students, has been charged with a felony count of dependent adult abuse resulting in death. If convicted, he faces nine years in prison.

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The law also requires bus drivers to receive training in child-safety check procedures every year when they renew their bus driver-safety certificate.