lxsw20: This all relies on the courier not dropping it at the door and leaving. I know from the doorbell camera, ours doesn't exactly stick around when dropping things off. Just drops it and runs. 

Same here, they get dinged of they spend more than three seconds delivering stuff.  I think a better, if somewhat ugly, option is to use a clothing bin style deposit system which is simple and quick to drop stuff into and doesn't require codes, keys, or anything else, just the ability to pull the deposit bin lever.