A co-worker of mine is on fire department...
He gave me a tour of their new truck they got today!
He showed me the trucks are plugged into air & electric full time while in the station.
He jumped up in the driver's seat and started the truck, and the air hose and extension popped off when he turned the ignition on.
Made by kussmaul, the outlet has a center pushrod plunger that's pushed in when you plug in... When the key is turned on, a solenoid is energized and releases the plunger to push the cord out.
Not sure how the air hose connection works yet, and this stuff may be old news... But, I thought it was pretty damned cool!
I guess the center ring pushes out and hits the outer ring on hose coupling...