A kind of detector is a device used to detect the presence of something. The crossword solutions for this term are LIE (3 letters), METAL (5 letters), and MOTION (6 letters). A LIE detector is a device used to detect deception by measuring physiological responses to questions. A METAL detector is a device used to detect the presence of METAL objects, such as coins or jewelry. A MOTION detector is a device used to detect movement in an area, usually used for security purposes.