Knock-Knock

 is a Quest in Escape from Tarkov.

Dialogue
"I solemnly present you with an assembled transponder! By the way, did you hear how Peacekeeper tried contacting with Lightkeeper? He's been pushing for a meeting for months, and he's still getting turned away. He even paid someone for a pass, but got a worthless piece of paper, though I don't know if it's true or not. But you were personally invited to the Lighthouse! How cool is that? Sic itur ad astra. So say hello to Lightkeeper for me. And good luck to you."

Objectives

 * Check if the transponder works
 * Escape Lighthouse alive

Rewards
"What do you mean, it didn't work?! What I make with my bare hands always works. Are you sure you had it on you? Oh well. I don't even know what to say. It's a good thing you're in one piece, at least. I'll try to figure out why that happened."
 * +31,300 EXP
 * Mechanic Rep +0.01
 * Lightkeeper Rep +0.01

Guide
In this quest you have to check if the transponder that the Mechanic gave you works. To do that, put the transponder in your inventory (can't be lost in a special slot) and walk up to the start of the bridge that leads to the lighthouse peninsula on Lighthouse. 

Ťuk-Ťuk Тук-тук, кто там?