What’s Inside Your Keyless Fob: Microchips, Antennas and Why They Matter

From the outside, it’s just a small plastic shell with a couple of buttons. Lightweight, slim, nothing remarkable. But open up any modern keyless fob and you’ll find surprisingly complex internals microchips, copper coils, antennas, transponders and even tiny quartz crystals. So what are they all for? Let’s break it down.

Antennas: More Than Just a Wire

The most visible part inside is usually a flat copper coil or a small wire loop. Believe it or not, this is what allows your fob to “talk” to the car.

In modern keyless systems, there may even be more than one:

1. A main coil for transmitting the signal when you press a button.
2. A passive radio antenna so the car can detect the fob even while it’s still in your pocket.
3. Sometimes extra antennas for NFC or Bluetooth, if your key supports features like “digital key”.

Without these carefully tuned antennas, the fob simply couldn’t send the correct frequency signal and the car wouldn’t know it’s yours.

Microchips and Controllers: the Brain of the Key

Every keyless fob contains a central microchip that manages everything:

1. Encrypting and encoding the signal to stop thieves intercepting it.
2. Detecting which button you’ve pressed.
3. Managing power consumption and waking the fob when needed.

The newer the car, the more advanced this chip usually is. Modern systems use rolling codes and encryption to keep the signal secure.

The Transponder: Why Your Car Starts

Many drivers think keyless means the fob alone opens and starts the car. In reality, there’s also a small transponder chip inside.

Even if your fob’s battery goes flat, the transponder still works. It’s powered wirelessly by an induction coil near the ignition switch or start button. Without this chip, the immobiliser wouldn’t let the engine turn over.

The Battery: More Critical Than It Looks

A CR2032 battery might seem simple, but there are details worth knowing:

1. The fob’s contacts are designed for a precise battery thickness.
2. Cheap batteries can struggle to deliver enough current, even when “new”.
3. Many new branded batteries (especially Duracell) come with an almost invisible protective film that must be removed or the fob won’t work.

Quartz Resonator: the Key’s Tiny Clock

Inside your fob there may be a tiny metal cylinder or square: a quartz resonator. This keeps the signal at exactly the right frequency usually 433 MHz or 868 MHz in Europe.

Without it, the fob’s signal could drift slightly and your car wouldn’t recognise it.

Why This Matters?

It’s easy to assume a fob is just “a plastic shell with a battery”. But really, it’s a miniature computer with its own antennas, power supply and encryption.

Which is why:

• Taking it apart casually can break delicate parts like the coil or circuit tracks.
• Using cheap batteries or replacement cases can cause faults.
• If your fob’s range starts dropping, or buttons become less responsive, it’s better to check it straight away rather than waiting until it fails completely.

How We Can Help?

At Phoenix Car Keys, we can:

1. Fit a new genuine case.
2. Replace the battery and measure current draw.
3. Repair damaged coils or quartz crystals.
4. Reprogram your fob or supply a car key fob replacement.

And most importantly, we’ll explain in plain English what went wrong and how to avoid it in future.