Yes
The total subject is "the device"; the simple subject is "device".
In the sentence, Joey saw a baby rabbit, Joey is the subject. Even though rabbit is a noun, it is in the object position. The word baby here is used as an adjective.
you
What is the subject of this sentence? She was the subject of an investigation.
No. A sentence must contain a subject and a verb. "Here's why" does not have a subject or a verb.
This is too bad. This is the subject in this sentence.
This is too bad. This is the subject in this sentence.
A sentence using the word subject: My favorite subject in school was Science.
It is a sentence. It is a declarative sentence also because it's giving a demand.
In the sentence 'Can you give a definition for that word?', YOU is the subject.
The pronoun they renames the subject noun 'friends'.
the subject is what the sentence is about