A radar detector is passive: it does not emit any radiation whatsoever.
It has been established that after "Black May", that the BdU perpetuated that Metox emissions were responsible for the losses. They could not accept the fact that the allies were able to operate Radar at 9cm.
Once a British bomber was shot down over Holland, and the H2S radar examined, that they realized that was the reason for the losses.
The Germans thought it impossible, they could not build a radar capable of 9cm wavelegnths,so they blamed the Metox.
Info from: The
U-Boat War by David Westwood. pp 206
