Certain types of wearables, like glasses, sunglasses, goggles, and headphones, only have a plural form.
Use a/an to introduce a single item for the first time.
She found a watch on the beach yesterday.
She found watch on the beach yesterday.
If the object has been previously mentioned or identified, you can use the article "the".
I bought a new fitness tracker this morning. The fitness tracker is compatible with this app.
We also use "a" or "an" to talk about something in a general way.
A smartwatch can record the route you take while exercising.
However, certain types of wearables, like glasses, sunglasses, goggles, headphones, and binoculars only have a plural form. They don't take the indefinite article "a" because "a" means a single thing.
Do you have sunglasses?
Do you have a sunglasses?
Note that all these objects consist of two parts. They are plural nouns, which cannot be used with "a".
I need to buy new headphones.
I need to buy a new headphones.
To count these items, you can use the expressions "a pair of", "two pairs of", etc.
I have two pairs of glasses in the drawer.
You can also use other determiners for plural nouns, like "some", "any", "the", "these", "several", etc.
These goggles are great.
But omit the determiner to talk about these objects in a general sense.
Sunglasses generally go well with most summer outfits.