Kenny McMillan's "TailGuardian" is a laminated printed strip that activates a "pull back" warning to drivers when approached within 25 yards.
Mr McMillan, of Irvine, has sold more than 10,000 of the locally produced devices to several bus companies, including Stagecoach and Arriva, and other commercial vehicle operators.
He said: "Since TailGuardian was fitted, a national bus company has reported a 60% decrease in buses being hit in the rear by other vehicles, with a consequent effect on repair and administration costs. I would imagine it has saved on insurance too."
A recent study showed that few car drivers know the correct braking distances at different speeds and even fewer (5%) could judge what these distances were on the ground. Most drivers (66%) underestimated the distance involved, some by up to 75%.
Mr McMillan said it had been harder to target private motorists, not only due to marketing costs but because car owners were reluctant to stick anything onto car bodywork.
"Consequently, I looked at the software and came up with an amended version that could be placed inside a car's slightly tinted rear window, which I believe will be a lot more acceptable."
TailGuardian uses filtering algorithms to enhance parts of the sign at the perception threshold, while remaining invisible outside the programmed distance.