What best fixes this sentence fragment At home?

You're absolutely right! "At home" is a prepositional phrase and a sentence fragment. Here are some ways to fix it, depending on the context you want to convey:

1. Add a subject and verb:

* I am at home.

* The dog is at home.

* Dinner is at home.

2. Combine it with a previous sentence:

* We went to the store, then came home. At home, we relaxed and watched a movie.

3. Use it as a dependent clause:

* While at home, I finished my homework.

* Because I was at home, I decided to cook dinner.

4. Add a word that makes it a complete thought:

* At home, I feel most comfortable.

* At home, I have my favorite chair.

To give you the best fix, please provide more context about what you're trying to say. For example, are you trying to describe where you are, what you're doing, or how you feel?