In my campaign, the paladin has to invoke a quick prayer to his god to use his detect evil abilities. This tones down the annoyance factor. I find it very unpaladin like to detect evil secretly anyway. A good paladin would let the person know that he was doing it, and then not understand why they get offended at it. He would see it as his duty, and assume people would be appreciative to his searching out evil within their midst.
TLG
