Question

The dog's master worked in the workplace. Later he came back home. He saw his dog. He said, "I'm home."
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Can we use 'I'm at home.' in this situation? What is the difference between them?
Writeacher
"I'm home," is a standard thing to say when one arrives home, whether from work or a long trip or whatever. It's similar to saying, "I'm here."

You'd use "I'm at home" if someone asks, "Where are you now?"