Detection is the act of noticing or discovering something. At the airport, you might see German Shepherds trained in the detection of drug smuggling or explosives in luggage.
Detection, detect, detective, detector — all are about noticing and discovering. A detective looks for clues that lead to the detection of the person who committed a crime. A metal detector is a machine created for the detection of coins people have left behind on the beach. Some teachers seem to have a third eye they use primarily for the detection of kids passing notes, or checking their cell phones during class.