Some of the first radar detectors were probably crude homebrew devices, made by ham radio enthusiasts. Before any known commercial radar detectors were available, the amateur radio magazine CQ published a design for a Radar Speedmeter Receiver in January 1958.
In the article, the author mentions that he doesn't approve of jamming the radar speedmeter "as it is very un-sportsmanlike"!
He says "A word to the wise is sufficient" and that "In this case, the word is a deep burp from the auto radio upon approaching a radar speedmeter, thereby reminding the driver to check his speed."
A few years later, a radar detector was available commercially: the Radar Sentry.