When I was IMing with another member we came up with the idea that some of us who are handy with electronics could perhaps design and build our own radar detector.
I know designing electronics for microwave frequencies can be tricky, so maybe an initial attempt we could scavenge a horn/LNA/LO/mixer/IF circuit from an existing RD, and then create our own firmware for it.
By doing so, we could tweak the RD with our own filtering algorithms, have it tweaked for certain Ka bands such as the dreaded 35.5. Or even create an unfiltered detector that alerts to every blip of radar (the ultimate highway warrior). Put two horns together to make our own "V1 clone", or use separate horns for each band, the sky's the limit...
I know if we were to make an RD to sell, we would have to deal with patents, FCC approval, etc., but for a one-off hobbyist project I could see it being feasible.
P.S. Another idea would be to create new firmware for an existing RD, to add features, change the filtering used, etc.