Some plural nouns refer to singular things but are made of many parts. Use a plural verb to go with them.
The scissors are good.
The sunglasses look fashionable on you.
The trousers fit him perfectly.
Those pants were a bargain.
However, when you talk of “a pair of scissors” or a “pair of sunglasses”, use the singular verb.
A pair of scissors is a good addition to a tailor’s kit.
A pair of sunglasses lies on the table.
Other such examples are: trousers, glasses, pliers, tongs, tweezers, binoculars, sunglasses, headphones, jeans, pyjamas, shorts, knickers.
Generally any tool, instrument or article of clothing which have two parts.