Typically, hearing aid devices use microphone technology to capture sounds and send signals wirelessly over an FM transmission (Frequency Modulation) or other transmission methods. We know…this is sounding a little like you should be breaking out the old transistor radio, and the technology isn’t all that different!
FM transmission systems do use radio signals to transmit sounds. These are great for public spaces.
Infrared transmission systems use light to transmit sound. Unlike other methods, this way signals cannot pass through walls. This is useful in places like schools or movie theaters. Infrared cannot be used outside or in placed with lots of bright lights as it cannot compete with too many light sources.
Having a personal amplification is useful in places where other transmission systems cannot perform. They are also great for low-noise environments such as car travel or watching television. They are about the size of a cell phone, and increase sound levels and reduce background noise for a listener.