This randomized experimental study (N=2,169) tested how different precautionary information formats about RF-EMF (with emphasis on 5G) affect public risk perception and trust in radiation protection authorities in Germany and Greece. Simple precautionary tips generally did not increase risk perception or reduce trust, while a conceptual explanation of the precaution/prevention distinction increased perceived risk compared with simpler information. Precautionary messages improved self-efficacy and perceived message consistency, and responses differed by country and gender.