A protection device, a wearable device, a protection method and a display system are provided. The protection device of the invention comprises a signal acquisition module, an information processing module, and a reminding module. The signal acquisition module acquires a determination signal, the information processing module processes and analyzes the determination signal acquired by the signal acquisition module and determines whether the users brain is in a state of fatigue, and the reminding module sends a reminder to the user based on the determination result of the information processing module. The protection device of the invention can monitor the degree of fatigue of a users brain and determine whether the users brain is in a state of fatigue, and then send a reminder to the user based on the determination result. The protection device of the invention can be applied to various wearable devices or display systems.
