• person or thing that detects; sensor
• a detector is an instrument which is used to find or measure something.
• polygraph machine, device used to determine the truth of a person's statements (based on changes in the person's respiration, pulse rate, etc.)
• device that detects the presence of metal
• device used to locate hidden explosives (in the land, sea, etc.)
• device used to detect the presence of ozone gas
• alarm system that is activated by a change in volume