The second component is an amplifier. It increases the intensity of the electrical signals. Filters in the amplifier modify the sounds, so that only the sounds needed by the person with the hearing loss are amplified. The third component is a loudspeaker. It changes the electrical signal, which has been amplified and filtered back into an acoustic signal, which the wearer hears.
Some hearing aids have volume controls and other controls, which can be used for adjustments.
Hearing aids require special batteries. The batteries are extremely small and may last from a few days to a few weeks, depending on the type of hearing aid and the amount of time it is used. Hearing aids require special care. They are built to be durable, but of course they can break if dropped on a hard surface. They may be damaged by water so they should not be worn in the shower or when swimming.