If the Deed takes place indoors, the Deed is considered done after you have left the building in which the Deed took place. All passengers need not have exited the building, but someone must hear you call Shotgun.
Some people choose to use a variation of this rule and require that all occupants be out of the building before Shotgun can be called. This does not work. It leads to everyone calling Shotgun at the same time and often ends in physical violence.