can someone explain to me why do they have earphones all the time they go to other floors?

there monsters that will come inside their ears and control them by audio hallucinations (if that's what they call it) cause if they talk to it they will ask what was their desires then control them

Correct me if im wrong but they always wear earphones because the audio can detect the monsters i believe.

The monster causes radio or comm interference so in the beginning they say you should call someone like just any number so that when the monster is near, it will get interfered and turned into beep beep noise like you're out of reach without connection instead of normal calling noise I think

OOHH THANK YOUUU NOW I UNDERSTAND HEHE (=・ω・=)

omg me too, thank you for the knowledge. Honestly, I was still at the beginning of the story, and I just guessed.