What's Inside a Car Key Fob? (And Why It Matters for Repair)
A non-technical look at the components inside a car key fob — what each does, what can fail, and what can be repaired versus replaced.
The Circuit Board
The brain of the fob. Controls all button functions and communicates with the transponder chip. Can fail due to water damage, impact, or age. Sometimes repairable; sometimes requires replacement.
The Transponder Chip
A passive RFID chip that communicates with the car's immobiliser when the key is near the ignition. Does not use the fob's battery — it's powered by the ignition antenna. Can survive circuit board failure in some cases.
The Antenna Coil
A small coil of wire that allows the transponder chip to communicate. If damaged (common in water-damaged keys), the car won't recognise the key even if everything else is fine.
The Battery
Powers the remote locking buttons. Typically a CR2032 coin cell. The transponder chip does not use this battery.
The Button Membrane
A rubber or silicone layer with conductive pads under each button. Over time the conductive carbon can wear away, causing unresponsive buttons — a common repair.
The Shell / Casing
Purely mechanical. Cracked or broken shells are the cheapest repair — we replace with a compatible aftermarket shell and transfer the internals.
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