SONAR
True basically in principle but this doesn't fit, and I think that the answer is ASDIC or Anti-submarine Detection Investigation Committee, the former US name.
A device for detecting underwater objects is typically called a sonar device. Sonar uses sound waves to detect and locate objects underwater by measuring the time it takes for the sound waves to bounce off the object and return to the device.
The Piranah Water 3000
sonar is a device for detecting objects underwater by emitting sound waves and analyzing the echoes that bounce back. It is commonly used in navigation, fishing, and underwater mapping.
Underwater sound detecting systems are called hydrophones. These devices are used to listen to and record sounds underwater, such as those produced by marine animals or underwater activities.
ASDIC
radar
e-nose
Sonar is used in various applications, including underwater mapping, navigation, fish finding, underwater communication, and military purposes such as detecting submarines. It works by emitting sound waves and analyzing the echoes to determine the location, size, and composition of objects underwater.
None. The megapixels are in the detecting device. e.g. a camera, a CCD device.
It's called a "Motion Detector"!
A Passive InfraRed Sensor (PIR)
Alexander Popov was one of the first to create a radar device. His device, created in 1895, was meant for detecting lightning strikes.