To perform an air brake alarm check, what should a driver do first?

Turning the ignition key to the "on" position is the first step in performing an air brake alarm check because it activates the truck's electrical systems and gauges. This action allows the driver to monitor the air pressure levels within the system, which is critical for ensuring that the air brakes are functioning correctly. Once the ignition is on, the driver can observe the air pressure gauge and listen for the low air pressure warning devices, ensuring safety before driving.

Other actions, such as releasing the brake, pressing the accelerator, or opening the windows, do not properly assess the air brake system's operational status. It is vital to establish that the air brakes are working correctly before taking any further steps in the process.