If you live in one of the hundreds of areas where multicolored luminous blobs zip around the night skies like giant fireflies with a glandular condition, you probably don't need a magnetic detector. But if UFOs are a rare sight in your community, there are only three ways to tell when they are coming. The first method applies only to psychics. If you have some latent or active psychic ability you may instinctively sense when a UFO is nearby.
Many people do.
These mysterious objects seem to have a strong connection with the psychic world around us. The second method is networking. In many places, people simply phone each other and spread the word that UFOs are buzzing around. If none of the above apply to you, you might try building a UFO detector. They are simple to make and they really do work.