I was thinking about the two phrases "I'm home" and I'm at home", and I agree, mostly, with the other answers. But I was trying to figure out why the first phrase even exists, if the other one is usually correct. I have some theories. Here are two different examples:
I'm home for the holidays.
You can say "I'm at home for the holidays", but it has a slightly different feeling; "I'm home for the holidays" means I'm in my hometown/neighborhood, but not necessarily in my own home. For example, a college student who has moved from his hometown of Boston, MA to Phoenix, AZ for college and currently lives in Phoenix can say he is "home" for the holidays if he stays with his best friend in Boston during the holiday break. He is not in his own home, or his parents' home, either, but is "home" in that he has returned to the area he came from. But if he says "I'm at home for the holidays" it could mean his home in AZ or his parents' home in Boston, but couldn't really include the best friend's place in Boston. You COULD say it, but it wouldn't be as clear or as natural as "I'm home for the holidays".
I'm home from work.
As the others mentioned, "I'm home" also is used to show arrival. If you are talking about where you are (and have been for any amount of time), you say "I'm at home". But when you're talking about your arrival, especially if you are talking to someone who is already there, you would say "I'm home". It feels sort of like "I'm home" is advising someone that you have arrived where they are, or where they expect you to be, whereas "at home" is telling someone your location when you could be anywhere.
Here is a silly story using I'm home and I'm at home in a bunch of different ways, so you can get the feel of it.
Betty and Bill went home to Colorado over the Christmas break. While they were there, Susan, Betty's co-worker, called Betty on her cell phone to wish her a happy holiday.
BETTY: Hello?
SUSAN: Hey, Betty, happy holidays!
BETTY: Hi, Sue! Nice to hear from you!
SUSAN: You too. I called your house, but nobody answered, then Ted told me you guys were out of town. Where are you?
BETTY:
I'm home visiting family; Bill's here, too, but Bobby
isn't home from school, he stayed in his dorm with his new college friends. Just me an Bill at home with my family.
SUSAN: Wow, that's fun. Denver, right?
BETTY: Yeah. It's cold.
SUSAN: I bet. Does your family have a fireplace to keep everyone warm in the Colorado winter?
BETTY: Oh, we're not staying with the family -- too many people. We're staying at the Sheraton. Since
we're only home for a few days, we figured we might as well splurge on a nice place and save the stress of having so many people in a small house -- almost all the
family are home right now. It's just too crowded.
SUSAN: Wow, I bet. The Sheraton! Whew, I wish I could've stayed at the Sheraton when I went to visit my parents. I had to
stay at home, in my old bedroom. Imagine, me and Ted in my old twin bed. THAT was tons of fun.
BETTY: Ha, I can imagine. Well, with Bill's Christmas bonus, we had just enough to bail us out of the crazy house and spring for the Sheraton.
SUSAN: Must be nice.
BETTY: Yeah...hang on, someone's on the other line....(after answering the other call)...Oh, that was Bill, calling to tell me
he'll be home soon. Yesterday
he wasn't home until almost 11, and I chewed him out for not calling. I guess he doesn't want that to happen again.
SUSAN: Haha, I can just imagine! Speaking of which,
Ted's at home right now waiting for me; I'm shopping for some stuffing. Can you believe he forgot? Anyway, he's expecting
me home soon, so I better hurry up. Just wanted to call and wish you happy holidays.
BETTY: Sure, thanks for calling. It was nice talking to you! See you next week!
SUSAN: Likewise. Alright, bye!
BETTY: Bye!
BILL: (From doorway) Honey,
I'm home!
BETTY: Did you remember the cranberry sauce?
BILL: Uhhhhhhh.....oops. Sorry.
So, language is fun and confusing, and the only way to get it, really, is to hear it used properly. I hope my little story helps some.
