Manfred Kaps, 44, was fed up with drivers racing down the Alten Landstrasse near his home in Hamburg, he told the Hamburger Morgenpost newspaper.
It only took an hour and a half to build the fake radar machine, using a length of rain pipe, a metal box and a Petri dish, he said.
“The whole thing didn't even cost me 40 euros,” he said. “It looks so real that it works.”
He said he feels that his eight-year-old son and 18-month-old daughter are safer now that more cars keep to the 60 kph speed limit past his house.
“This street leads to school and kindergarten. But it does not seem to interest the drivers. The limit is 60, but despite this they are always racing.”
The paper reports that because Kaps' fake speed radar does not emit a light which might endanger traffic, he has not broken the law.