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.
ASDIC
The Piranah Water 3000
ASDIC
Sonar
radar
e-nose
None. The megapixels are in the detecting device. e.g. a camera, a CCD device.
Sonar is a method of detecting underwater objects with sound pulses-like radar but with sound not microwaves
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.
A microphone detects sounds transmitted in the air.