微波听觉效应，又称弗雷效应，是指由脉冲或调制微波作用于人脑时，会产生出可听喀嚓声（或经过调制处理的完整字词）的现象。由于喀嚓声是直接在人脑中生成，因此不需要任何电子接收设备。这个效应最早的报告，是出自二战期间在雷达询答器附近工作的人员。这种效应导致的声音附近的其他人是听不见的。后来发现微波听觉效应是由电磁波谱中，波长较短的无线电波所引起的。在冷战期间，美国神经学家艾伦·H·弗雷(Allen H. Frey)研究了这种效应，并且成为第一个发表微波听觉效应的人。

根据现时所被接受的机制解释，这是因为人脑受到微波脉冲的急速加热（辐度很小，约在十万分之一摄氏度），产生了压力波，然后经头骨传到耳蜗，所以就生成了听得见的声音。

The Microwave Auditory Effect, also known as the microwave hearing effect or the Frey effect, consists of audible clicks (or, with speech modulation, spoken words) induced by pulsed/modulated microwave frequencies. The clicks are generated directly inside the human head without the need of any receiving electronic device. The effect was first reported by persons working in the vicinity of radar transponders during World War II. During the Cold War era, the American neuroscientist Allan H. Frey studied this phenomenon and was the first to publish information on the nature of the microwave auditory effect.