"Who's there?" I heard.

“谁在那里？”我听到回应。

youdao

Very softly, she called out: "Hello? Who's there?"

她很轻柔地喊道：“喂？谁在那儿？”

《柯林斯英汉双解大词典》

A call came from a window, "Who's there!"

一个喊声从窗口传来：“谁在那儿！”

youdao

The old man sat up in bed, crying out "Who's there?"

VOA: special.2009.05.16

What is it for that person who's there on Thursday to be the same person as the person who's sitting here lecturing to you today?

这意味了什么,周四和今天在这给你们上课的是同一个人,是同一个人？

耶鲁公开课 - 死亡课程节选

Yeah, yeah, you know like, there is always, you know, the issue where there's a lot of students who want space

是，是，你知道，总是这样，你知道，问题在于那么多学生都需要空间，

学生会馆的实习部门 - SpeakingMax英语口语达人

He's a man who's there to serve his country, and not just his party.

NPR: Transcript: Gov. Sarah Palin At The RNC

The slob hooks up at a bar with a gorgeous blonde who's there to celebrate a big promotion.

WSJ: Film Review

There's no word on the quality of the camera onboard, however, its infared-equipped, so you'll be able to see who's there at night.

ENGADGET: DoorBot lets you see and talk with who's at the door from the comfort of your smartphone (video)