Yup....very illegal in Ireland! I have personally seen the gardai take one from a foreign registered car driven by a tourist. No amount of protesting or claims of ignorance held any water and the tourist was told he was lucky he wasn't taken down the station for questioning.
Any suggestions? yes... along the roads, there are circular signs with a red perimeter and a number written on it an. They indicate the speed limit.....So, reading them and paying attention while driving saves you money as you do not need to fork out on a detector . Added feature is that it also saves lives.