In chapter 3 of Life Is Strange you will be tasked woth breaking into the principals office. After blowing up the pipe bomb to gain entrance to the principals office the fire alarm will go off and you will need to disable if before you have to rewind time. The solution to this is obvious when you see it but is quite tricky to figure out.
Start by blowing the door open and this will set off the alarm. Go inside the principals office and rewind time inside his office. This means you will now be inside the office before you set off the pipe bomb and the fire alarm. You can now open the door to let Chloe inside.