My favorite gadget is my watch, because it tells me the right time when to go to school. When I play, it tells me when I should go home. So, my favorite gadget is my watch.

Rachel: My favorite gadget is a watch, because when I see my watch, it tells me time to go to school.
Correct: My favorite gadget is my watch, because it tells me time the right time when to go to school.
Explanation: Since you are talking about a specific thing, you can use the possessive pronoun my to show that it's yours.

Rachel: or when I play, it tells me when I should go to my home.
Correct: When I play, it tells me when I should go home.
Explanation: The sentence is clear without it.