Passengers are being reminded that one of the most common habits in the air—something many people do without thinking—can cause serious trouble on a United Airlines flight. No shouting, no drunken scene, no fight in the aisle. The problem could simply start with your phone.

Playing music, movies, games, or other audio through your device’s speakers can disturb an entire cabin. United has reminded travelers that entertainment should be enjoyed using headphones or earbuds rather than forcing everyone nearby to listen along. What seems like a harmless few minutes of scrolling can quickly become a problem if a passenger refuses to cooperate.

And that refusal is where things can escalate. Flight attendants are responsible for maintaining order and enforcing crew instructions. If someone repeatedly ignores a request to stop playing audio aloud, the situation may go beyond a simple reminder. Before departure, continued refusal to follow crew instructions can potentially result in the passenger being removed from the aircraft.

That doesn’t mean accidentally playing a video for a few seconds will automatically get you kicked off a flight. The key issue is what happens after the crew asks you to stop.

So before settling into your seat, there’s one small item worth keeping within reach: headphones.

Air travel already means sharing a tight space with hundreds of strangers. A little consideration can make the journey easier for everyone—and prevent a simple phone habit from becoming a very expensive travel mistake.