Using your left thumb on the joystick, walk directly toward the low ceiling or vent. Do not stop.

You cannot crouch in the middle of an open hallway just for fun. You must approach a specific obstacle. The first time the game forces you to learn this is in the Schoolhouse section, just before encountering the Statues mini-game. Look for:

In Chapter 2, the mechanic is vital for two primary reasons:

Subject: How to Execute the Crouch Action Platform: iOS / Android Status: Confirmed Control Scheme

Later in the game, specifically during the Statue chase sequences and in the Factory hallways, you will encounter red laser tripwires stretched across hallways at ankle height.

If you are frantically tapping your screen and still getting hit by a monster, check for these three common problems.