CROS/BICROS

Used for unilateral hearing loss (CROS), or for hearing losses in which the loss in one ear is significantly greater than the other (BI-CROS). Specifically, these are used when one of the ears cannot benefit from a hearing aid.
A microphone is placed on the poorer ear and the signal is then routed to a hearing aid on the better ear. This provides sound from the “dead” or unusable side.