Pendulums are used in simple divination work to answer yes or no questions or more complex questions with the use of a mat.  There are different ideas as to who or what is controlling the swing of the pendulum.  Some believe it is the higher self, who is in direct contact with the divine, that answers your questions through the movement of the pendulum.  Others believe it is the spirit of an ancestor, a god or goddess, angel, or other guide.