Barney is drilling into a safe (or breaking into an office, or...) with an elaborate device that took several minutes to set up, when he hears a guard turning the doorknob and about to catch him! Music sting, Fade out to commercial.
Fade up from commercial: The door opens! The guard steps in, looks around. We see no one. The guard shrugs and leaves. Cut to Barney and his equipment - he's somehow managed to get into the overhead air duct with everything, without making a sound, in the time it took the guard to turn the knob and open the door.