I have recently come to understand there are technologies, like a kind of wireless waveform, pressure wave, or frequency triangulation that can interact with physiological states and neurons, can transmit audio or concepts, images, and ideas, direct into the psyche and can receive data of a similar type... apparently mostly receives language and not so much non-lingual ideation.
Don't, however, let this make you paranoid. If this is happening to you it will at some point start to become obvious. You will often hear a ringing in the ears, feel a shifting of a energetic focal point around the cranium accompanied by a change in frequency, hear whispering or slowly spoken phrases or key word commands by users of the device.