By Amy Lester, NEWS 9

OKLAHOMA CITY -- It's something parents don't ever want to hear; their child was left for hours, alone on a school bus. The Oklahoma City School district is taking extra steps to make sure that doesn't happen.

Over the past three years twice a student has fallen asleep in a seat and left alone on a school bus. The students were later found at the district's bus barn. The district said that's two kids, too many.

Parents put their trust in bus drivers and that is a responsibility Tonda Russell takes seriously.

"Our number one job is to pick up and deliver children to school safely," Russell said.

In more than 25 years, she's never left a child alone on board. She understands why it happens.

"You can put 65 kids on this bus and you'll think with all your heart that you saw each and every one go off and there could be that small little one that's tired, in the seat, asleep and you missed him," Russell said.

Russell said a quick glance isn't enough.

"When I'm sitting here, I don't see any children. When I stand up, I still don't see any children," she said.

When she walks the aisle, she realizes, someone's there. Drivers are supposed to check at the end of each route, but sometimes don't.

"There's incidents throughout the U.S. that when this occurs, sometimes it does end up with a bad result," Stephen Foster, Director of Transportation, said. "So, our goal is just to promote further safety for the students."

That's why the district is installing No Child Left Behind alarms. When bus drivers turn off the ignition a buzzer goes off to remind the driver to check the bus. To shut the off, the driver must walk to the back of the bus to open the back door. If the driver does not do this, the horn will honk and the lights will flash indefinitely.

"That extra security that their child will be checked on, as a parent, I would want that," Russell said.

The alarm is loud and will keep sounding until someone does the safety check, or the horn burns out.

The alarms cost $35 each and the district is paying for them out of its transportation budget.