"Headphones" is a plural noun. Some English nouns, like headphones, only have a plural form and are grammatically plural.
"Headphones" is a plural noun or plurale tantum (Latin for "plural only"). Some English nouns, like headphones, only have a plural form and are grammatically plural.
Put on your headphones.
Put on your headphone.
These nouns cannot be used with numbers or the indefinite article "a" ("a" means a single thing.) However, you can make them countable by introducing the expressions "a pair of headphones", "two pairs of headphones", etc.
He bought a new pair of headphones last Thursday.
Plural nouns require a plural form of a verb, so we say "headphones are", not "headphones is".
Your headphones are on the bed.
Your headphones is on the bed.
They also take a determiner or pronoun (these, those, they, etc.) in the plural.
Where did you buy these headphones?
Follow the same strategy with these plural nouns: