🔧 Key Fob How-To Guides

Open the fob (usually with a small flathead screwdriver in the seam or a coin in a slot) and look at the battery. The type is printed on it — most car fobs use CR2032 (20mm diameter, 3.2mm thick) or CR2025 (thinner). A few older fobs use CR1616 or CR2016. If you're not sure, check your owner's manual — the battery type is listed in the key fob section.

Yes, for many vehicles made from the late 1990s onward, there is a self-programming sequence you can do from the driver's seat — it typically involves inserting and removing the key in a specific pattern while pressing fob buttons. However, some car brands (notably BMW, Mercedes, and most European vehicles after 2010) require dealer-level OBD programming. Our full programming guide covers both methods.

Replacing the battery often causes the fob to lose its pairing (sync) with the car. The fix is a re-sync: most cars have a self-programming sequence you can do in a few minutes. If the fob still doesn't work after re-syncing, the issue may be a faulty battery (even brand-new batteries can be dead), incorrect installation (battery orientation), or physical damage to the circuit board inside the fob.

Relay theft is a method where two thieves use a signal amplifier to extend the range of your key fob from inside your home, fooling your car into thinking the fob is nearby and unlocking the door. It now accounts for over 50% of keyless car thefts in the UK and is rising sharply in the US. A $10 Faraday pouch completely eliminates this risk by blocking the fob's signal when stored at home.

Most vehicles have a "fob deletion" step in the programming sequence — you enter programming mode and either delete all fobs and re-register the ones you still have, or (on newer vehicles) delete individual fob IDs via the infotainment system under Settings → Key Fobs or similar. If you can't do this yourself, a dealer or locksmith can clear all programmed fobs and reprogram your remaining key.

A traditional key fob requires you to press a button to lock/unlock the car — it only communicates when you press the button. A smart key (also called a proximity key or passive entry key) continuously broadcasts a low-power signal. The car detects the smart key when you touch the door handle and unlocks automatically, without any button press. Smart keys are more convenient but also more vulnerable to relay theft.