microcontroller alarm device

When a school bus arrives at the school after picking up the students the bus driver or bus attendant is supposed to check whether any students are left behind by going upto the back seat of the bus after every trip. But sometimes the drivers forgets or just dont want to walk upto the back seat. We want to avoid such a situation. We want to develop a controller that will trigger the horns on and the bus door open so that any student left behind can get out of the bus. The idea is to install a switch at the back seat of the bus. So every time the driver turns the igntion off, he should go to the back and depress the switch. This way we can make sure the driver has actually gone upto the back seat of the bus. If he doesnt depress the switch after 30 seconds the controller should trigger horn and doors open. Workflow 1. School bus comes to stop at the school and bus driver switch the ignition off 2. He walks to the back seat to depress the alarm switch off 3. If he doesnt depress the switch off after 30 seconds the controller should trigger horn alerts, flash lights on and doors open 4. Driver return to depress the switch to trun off the alarm. We want the device to be designed and atleast 10 workable prototype to be produced ASAP. Please chat with me for clarifications