Heard a quote from Obama tonight that got me to wonder:
Is there a “key” to the White House? When I leave my house, I lock the door and to gain re-entry, I need a key (Or the high tech equivalent). So when Bush (or whomever) leaves the house and returns, does he need (or his SS detail, whoever) need to use a key to re-enter, or is there always a staff on hand to open 'er up for the resident in chief?
The White House is staffed 24/7 by both staff and Secret Service. No one needs to carry a key, and since there’s an armed guard at all the entrances, you can leave the doors unlocked. 
Well there is the public White House and then there is residence, where the POTUS and family hangs out. I’m guessing that some of the doors have locks, but the Prez doesn’t have the keys on him.
Did Bill lock the door to the Oval Office or did he just close the door?
I think the OP might possibly have an incomplete perception of what the White House really is. It’s not just a house where the President lives. It’s more like a big office building whewre much of the building is given over to the president, his staff and adisors, etc. and the actual residence is confined to a small section of the building. There is no time when the whole builiding is just shut down with the lights turned off and the security system turned on. There are always people there and lots of them have guns.
or perhaps I understood that but failed to specify to your understanding, that my question is "does the Prez (or whoever) need to carry a “key” (or high tech equivalent) to gain access to the (private residence part of the) White House?
better?
Maybe you do need a key - link