Many travelers take extra precautions when checking into a hotel room, and one surprisingly simple safety tip has recently gained attention online. Flight attendants and security experts suggest tossing a water bottle under the bed as a quick way to check whether anyone might be hiding there. The idea is simple, easy to remember, and can be done within seconds of entering a room.

The method works by rolling a water bottle under the bed from one side. If the bottle rolls freely and comes out on the other side, the space is likely clear. However, if it suddenly stops, hits something, or rolls back toward you, it could indicate an obstruction underneath. While there may be an innocent explanation, it can also serve as a warning sign that deserves further attention.

Travel safety advocates say the trick offers two important advantages. First, it allows guests to inspect the area without crouching down and putting their face close to the bed frame, which could leave them vulnerable if someone were hiding there. Second, it provides an early warning that something may be wrong, giving travelers the chance to leave the room immediately and contact hotel security rather than confronting a potential intruder themselves.

The tip works best with beds that have enough open space underneath for objects to roll through easily. If a bed has a solid base or extends all the way to the floor, the method will not be effective. In those situations, experts recommend manually checking common hiding spots such as closets, bathrooms, and other areas before settling into the room.