Tests such as MRI's and x-rays both detect implants. Dental x-rays are also known to reveal implants. When discovered on MRI's or x-rays, medical staff will not necessarily bring these unexplainable objects to the attention of the patient. Implants may be composed of a variety of metals or other materials found on Earth. However, the underlying atomic structure of the molecules wrapped with other substances may be a technology not yet known to exist on Earth.
Some implants form a bump under the skin.
Upon having the bump removed, people learn that it contained a softer, spongy material of unknown origin. Most people are at a loss to conjecture about the purpose of such a spongy material. Based on their metallic qualities, it is speculated the implants may be transmitters, receivers, tracking or communication devices. As a transmitter, information could be sent from the Aliens to the abductees alerting them to an impending abduction. Information transmitted could wake the abductee up to a conscious level, a particular dream level, or to an out of body state.