pendulums have been used as ancient divination tools for many, many years. The idea behind the pendulum is that is can bring subconscious energy into conscious awareness to give you answers to questions you may have.
This is possible because there is energy in everything, the energy within us runs through our arm and down through the pendulum. They can help you gain insight by asking them yes or no questions and seeing how they respond. They help to bring unconscious energy into conscious awareness.