If options are available, staff should always ask visitors which device they need or prefer. Also, staff who dispense ALDs need to be trained in their use and maintenance. Maintenance may include routine equipment checks and recharging batteries. The transmitter picks up the sound and converts it to a signal, which it then sends out. The receiver picks up a signal and transmits it to the visitor.
Several receivers can pick up the signal from a single transmitter.
Infrared systems transmit sounds via light waves to users wearing receivers. The receiver must be in the transmitter's line of sight to function properly. This limits where visitors with receivers can be located, but it also prevents spillover of sound into other areas. IR systems are often used in movies, conferences, and live performances. FM systems transmit sounds via radio waves.