How Car Keys, Key Fobs and Push-Button Start Work

Three jobs, one key

A modern car key can do three separate things: the metal blade turns the locks, a chip tells the car it's the right key, and the buttons work the locks from a distance. They're separate systems, which is why one can quit while the others keep working.

The chip: transponder keys and the immobilizer

Most cars built in the last 20-plus years have a small chip in the head of the key called a transponder. It doesn't need a battery. When you turn the key, a ring-shaped antenna around the ignition sends out a signal that powers the chip, and the chip answers with its code.

If the code is on the car's list, the engine is allowed to start. If it isn't, the immobilizer either stops it from cranking or lets it crank but won't let it run. A flashing security or key light on the dash is often the first sign the car doesn't recognize the key.

Remote fobs

The lock and unlock buttons send a short radio signal to the car. Most use rolling codes, which change every time you press a button, so someone can't record the signal and replay it. This part does need a battery, usually a coin cell.

Smart keys and push-button start

With a smart key, the fob can stay in your pocket. Antennas around the car sense it when you're close, unlock when you touch the handle, and let you start with the button. Because the car is looking for the fob by radio, a dead fob battery can leave you stuck. Many cars can still read a dead fob if you hold it right up to the start button or a marked spot, so check your owner's manual.

Why a new key has to be programmed

Cutting a blade to fit your locks is only half of it. The car only starts for keys on its list, so a new chip key or fob has to be programmed to your car with the right equipment. We do that on site, usually for less than the dealer.

Simple ways to tell what's wrong

• Range getting shorter, or you have to press twice: the fob battery is getting weak.
• Buttons quit but the car still starts: it's the fob's battery or remote, not the chip. The chip doesn't use the battery.
• Cranks but won't start, with the security light flashing: the car isn't recognizing the key's chip. Try your spare. If the spare works, the problem is the first key.
• "Key not detected" on a push-start car: try a new fob battery, or hold the fob against the start button.
• Key won't turn in the ignition: turn the steering wheel a little while you turn the key. The steering lock may be holding it.
• Lost every key: call us with the year, make and model, and we'll tell you what it takes to get you going.

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