noun
detector; detecting device
General term for a device or machine that detects something, such as gas, metal, or radiation.
ガス発見器が警報を鳴らした。
The gas detector sounded an alarm.
金属発見器でコインを探す。
Search for coins with a metal detector.
Compound of 発見 (はっけん, 'discovery, detection') and 器 (き, 'device, instrument').