Or, worse, when someone has left the organization and the organization hasn’t bothered to put up an OOO, so I’m just emailing a blackhole until I call or someone finally checks that inbox. I never fail to set up my OoO reply, and yet most of my external contacts don’t get them. Let’s say I work for LlamaCombs, with an name(@)llamacombs.com address, and this is a company who has two clients AlpacaBrush and VicunaShampoo. I work primarily with the second, and their internal directory lists my contact info as name(@)vicunashampoo.com. It works because any e-mail sent to the second address is auto-forwarded to the first. Except it messes up OoO replies big time. Because the auto-reply is sent to my own alternate address, not to the original sender, and I have no way to change that.
I think people still understand that out of office can refer to home office as well. But you could say “unavailable” or “away from work”.

“Hi, I’m Troy McClure!” We’re not sure who wrote the original Troy McClure out of office message, but this version by Paul Sokol of Infusionsoft is a real gem.
But what if you’re only taking off one day? Sometimes, it might seem silly to bother with an out-of-office for such a short amount of time–especially if it’s a day that a lot of other people are taking off (such as a national holiday). If people do need you to get back to them urgently, they’ll think they’re being ignored. (Even if you define “urgently” differently.) And if there’s a chance of an emergency landing in your inbox, it’ll be that much harder for you to unplug because you’ll just keep “checking in.”