There are four common types of in-the-ear hearing aids that you will find online or at an audiologist.
Invisible In The Canal (IIC) - This tiny style sits inside your ear canal with only a pull tab visible to remove the device.
Completely In Canal (CIC) - The top of the hearing aid is visible to those looking from the side, but the device is very discreet.
In The Canal (ITC) - Comfortable but visible. More easily accessed to change the volume or mode.
ITE: This style is even more accessible and allows for more power and, in some cases, rechargeability and Bluetooth.
Most people who prefer invisible hearing aids will gravitate towards IIC or CIC styles.