You are allowed to bring what you want with you TO the test center (but, remember, you’ll have to lock everything up in one of the provided lockers. Thus, make sure what you bring will fit into a small space).
You can bring study notes, cell phones, lunch, snacks, etc.
THE EXAM ROOM: You may NOT bring any documents, materials, machines, or electronic devices (including computers, telephones, recording devices, cameras, and typewriters) into the examination.
Before you enter the exam room itself, you will be searched (metal detector), pockets turned inside out, etc. Prometric does not want you to bring ANYTHING into the room except that which they give you (which is typically a few pencils and pieces of paper).