People or things that make loud, high-pitched sounds, like when they are very scared or excited.
Shriekers are usually very loud and can be a little scary.
Examples:
The children are shriekers when they see the spider.
The sirens are shriekers when they go by.
The shriekers run away from the big dog.
The monkeys are shriekers when they get bananas.
The movie is full of shriekers when the monster appears.
The birds are shriekers when they see the cat.