Hearing aids have been around for well over a century, evolving from bulky, trumpet-shaped devices to the sleek, near-invisible gadgets people wear today. They remain one of the most widely used medical devices on the planet, helping hundreds of millions of people reconnect with the sounds and conversations they had been missing.
Despite how common they are, most people have never really looked at what goes on inside (and outside) one of these little devices. You might wear one every day or be considering one for the first time, and still have no idea what each tiny piece actually does. That gap in knowledge can make the whole experience of buying, fitting, and maintaining a hearing aid feel a lot more confusing than it needs to be.
The truth is, once you understand the basic parts and how they work together, everything else clicks into place — from choosing the right model to troubleshooting small issues on your own. That is exactly what this guide is for.
Hearing Aid Parts Diagram & Details
The diagram featured here shows a behind-the-ear (BTE) hearing aid, which is one of the most popular styles used worldwide. The main body of the device — a curved casing that sits snugly behind your ear — houses most of the electronic components. From there, a thin plastic tube extends downward and connects to a custom-shaped mould that fits inside your ear canal. Labels point to eight distinct parts spread across the device: the sound hook at the very top, microphone openings along the upper edge, an LED indicator on the side, a push-button/volume control on the back panel, the battery door at the bottom of the casing, the plastic tube running from the hook down to the mould, and a sound outlet at the tip of that mould.
Each of these parts has a specific role in capturing, processing, and delivering sound to your ear. Let’s walk through every one of them so you know exactly what you’re looking at — and why each piece matters.
1. Sound Hook
The sound hook is that small, curved piece sitting at the very top of the hearing aid where the main casing meets the plastic tube. It acts as the bridge between the electronics inside the device and the tubing that carries amplified sound down into your ear. Without it, there would be no way for processed audio to leave the casing and reach you.
Most sound hooks are made from hard, durable plastic, and they are shaped with a gentle curve that mirrors the natural contour of the top of your ear. This design helps the hearing aid stay anchored in place throughout the day. On many models, the hook is removable, which makes it easier to replace if it cracks or gets damaged over time — something your audiologist can handle in minutes.
What a lot of people don’t realize is that the sound hook also plays a subtle acoustic role. Its internal diameter and length can influence the tone quality of the sound reaching your ear, and some audiologists will swap hooks of different sizes to fine-tune the listening experience for a particular user.
2. Plastic Tube
Running from the sound hook all the way down to the earmould, the plastic tube is the pathway that carries amplified sound from the hearing aid’s body into your ear canal. It is typically made from soft, flexible, medical-grade tubing that is both lightweight and comfortable enough to wear for long hours.
Over time, this tube can harden, yellow, or develop moisture buildup inside it — all of which can muffle the sound quality you’re getting. That’s why hearing care professionals recommend replacing the tubing every few months, or as soon as you notice it stiffening up. It’s a quick, inexpensive fix that can make a surprisingly big difference.
The length of the tube is trimmed during your fitting appointment so it matches the distance between the top of your ear and your ear canal perfectly. If it’s too long, the hearing aid will feel loose and look awkward. Too short, and it will tug uncomfortably. Getting that fit right is a key part of why professional fittings matter.
3. Microphone Openings
Near the top of the hearing aid’s casing, you’ll find one or two tiny openings — these are the microphone ports. They’re where all sound enters the device before being processed and amplified. Every voice, every bit of music, every car horn — it all starts here.
Modern BTE hearing aids often feature two microphone openings working together in what’s called a directional microphone system. One microphone focuses primarily on sounds coming from in front of you, while the other picks up sound from around and behind you. The hearing aid’s processor then compares the two signals and emphasizes the sounds you’re most likely trying to hear — like the person speaking across the table — while dialing down background noise.
Keeping these openings clean is one of the simplest and most important maintenance tasks you can do. Even a tiny bit of dust, earwax residue, or lint from your clothing can block the ports and dramatically reduce your hearing aid’s performance. A soft, dry brush — usually included with the device — is all you need to clear them out each day.
4. LED Indicator
On some hearing aid models, a small LED light is built into the side or edge of the casing. This indicator serves as a quick visual status update, letting you (or a caregiver) know what the device is doing at a glance.
Depending on the manufacturer, the LED might flash or change color to signal different things: a green light when the device powers on, a red blink when the battery is running low, or a blue pulse when it’s connected to a Bluetooth-enabled phone or streaming device. It’s a small feature, but it can save you from that frustrating moment of wondering whether your hearing aid is actually on or whether the battery just died.
Worth noting: not every hearing aid has an LED indicator. It tends to appear more often on mid-range and premium models. If the idea of a quick visual check appeals to you, it’s worth asking about during your fitting consultation.
5. Sound Outlet
Located at the very tip of the earmould — the part that sits deepest inside your ear canal — the sound outlet is where amplified sound finally exits the system and reaches your eardrum. Think of it as the final stop on the journey that began at the microphone openings.
Because of where it sits, the sound outlet is highly prone to blockage from earwax. Most hearing aid manufacturers include small wax guards or filters that snap over the outlet to prevent buildup from reaching the internal components. These filters are disposable and should be changed regularly — your audiologist will show you how during your first fitting.
A blocked sound outlet is actually one of the most common reasons people think their hearing aid has stopped working. Before assuming something is broken, checking and cleaning this small opening is always the first troubleshooting step any professional will recommend.
6. Push-Button / Volume Control
On the back or side of many BTE hearing aids, you’ll find a small push-button or rocker switch. This gives you manual control over certain settings — most commonly volume, but sometimes listening programs as well.
Pressing the button might cycle through different sound environments: one mode for quiet conversations, another for noisy restaurants, and a third for streaming music. A quick press might raise the volume, while a long press switches between programs entirely. The exact behavior depends on how your audiologist programs the device to suit your lifestyle and preferences.
That said, this feature is labeled “optional” on the diagram for a reason. Many newer hearing aids are designed to adjust automatically, using onboard sensors and algorithms to detect your environment and adapt in real time. Some users prefer that hands-off experience and never touch a button all day. Others like having the ability to fine-tune things manually. It’s a matter of personal preference, and most audiologists will set up whichever approach suits you best.
7. Mould
The mould (also spelled “mold”) is the custom-shaped earpiece that sits inside the bowl and canal of your ear. It’s the part that anchors the hearing aid in place and creates a seal so that amplified sound is directed efficiently into your ear canal rather than leaking out.
Custom moulds are usually made from an impression of your ear — your audiologist takes this impression during one of your first visits by filling your ear canal with a soft, quick-setting material. The result is a mould that fits your unique ear shape with precision, which is why wearing a properly fitted hearing aid shouldn’t cause soreness or discomfort even after a full day.
Moulds come in different materials, including hard acrylic and softer silicone. Softer materials tend to provide a more comfortable fit and a better seal, especially for people with higher levels of hearing loss who need to prevent sound from escaping (which can cause that annoying whistling feedback). Your hearing care provider will help you pick the right material based on your hearing needs and comfort.
8. Battery Door
At the bottom of the hearing aid casing, you’ll find the battery door — a small hinged compartment that holds the device’s power source. Opening it lets you insert or replace the battery, and it also doubles as an on/off switch: closing the door powers the hearing aid on, and opening it turns it off.
Most traditional BTE hearing aids use tiny zinc-air disposable batteries that come in color-coded sizes (the most common being size 13 or size 675 for BTE models). These batteries are activated by removing a small adhesive tab, which exposes them to air and starts the chemical reaction that generates power. Depending on your usage and the hearing aid’s power demands, a single battery can last anywhere from five to fourteen days.
Many newer models are shifting to built-in rechargeable lithium-ion batteries, which eliminate the need for a battery door altogether. With rechargeable devices, you simply place the hearing aid in a charging cradle overnight — much like charging a smartphone. If the idea of fiddling with tiny batteries isn’t appealing, a rechargeable model might be the better fit for your routine.
