Automatic Very Low Frequency (VLF) ground canceling metal detectors have proven to be the best all-around choice for ground (land) searches in law enforcement applications. This is because of their ease of use and sensitivity. They automatically tune themselves to the characteristics of the ground being searched (automatic ground canceling). Although the VLF detector must be kept in motion to detect a metal object, very little motion is required for most of the VLF detectors. For extremely deep searching for large objects on land, specialized metal detectors known as "two-box" metal detectors may be used. A large object such as an automobile may be detected as deep as 20 feet. Detectors manufactured for underwater use are specially designed to allow the entire metal detector, including the control housing, to be completely submersible. Some detectors may be submerged to several hundred feet or more. Pulse induction metal detectors for underwater searching ignore black sand and salt water, which can affect the sensitivity of some types of metal detectors. All automatic VLF ground canceling metal detectors and a few pulse induction metal detectors have the capability of selectively eliminating undesirable objects from detection. This article discusses the factors that affect detection depth and coverage, the importance of using the appropriately sized searchcoil when processing a crime scene, the selection of a metal detector, the role of metal detectors at crime scenes in relation to other methods of detecting evidence, and training in the use of metal detectors.