at death's door
• (especially in hyperbolic use) so ill that one may die.
• "you've been out a lot, considering you're supposed to be at death's door"
on the door
• monitoring admission to a building or event.
• "the uniformed commissionaires on the door"
• on admission to an event rather than in advance.
• "they were going that night to try and buy tickets on the door for a comedy show"
