Smart keys and push button start, explained without the jargon

A smart key, also called a proximity key or intelligent key, is a fob that talks to the car by radio. You do not insert it into anything. Sensors in the car listen for the fob, and when it is close enough, the car allows you to unlock the doors by touching a handle and to start the engine by pressing a button on the dash while your foot is on the brake.

Underneath that convenience are two separate conversations. One happens at the doors and trunk, where short range antennas check whether a valid fob is nearby. The other happens at the push button, where an antenna inside the cabin checks for the fob and the car's immobilizer decides whether to allow the engine to run. Both depend on the fob answering correctly.

If you want the bigger picture of key types before reading on, our guide to car key types in plain words places smart keys alongside plain, transponder and remote head keys. The relationship with the chip based system is covered in transponder keys explained.

When you touch a door handle or press the start button, the car sends out a low power radio request from antennas placed around the vehicle. A fob that is in range hears the request and replies on a separate frequency with a coded message. The car checks the code against the keys it knows. If it matches, the doors unlock or the engine is allowed to start.

The range is deliberately short, typically a few feet around the door or inside the cabin. That limit matters for security. A car should not unlock because a fob is across the street. The cabin antennas are also arranged so the car can tell whether the fob is inside the car or only outside the door, which is why it will warn you if you step out with the engine running and the fob left on the seat.

The codes change. Modern systems use rolling or encrypted codes so that a recorded signal from yesterday cannot be replayed today. That is part of why programming a replacement is not as simple as copying a number. The new fob has to be introduced to the car in a way the car trusts.

Pressing the start button does not directly start the engine. It sends a request to the car's control units. The car first checks that the fob is inside the cabin. Then it checks other conditions, such as whether you have your foot on the brake, whether the transmission is in park or neutral, and whether the immobilizer accepts the fob. Only then does it crank the starter.

The sequence explains several everyday problems. If the car says it cannot find the key, the fob battery may be weak, the fob may be in a place that blocks the signal, or the cabin antenna may be struggling. If the car will not start but the dash lights come on, the brake switch or the transmission position may be the cause rather than the key.

Many cars have a backup way to start. When the fob battery is dead, the owner manual usually shows a spot where you hold the fob against the start button or a marked area in the cabin, and the car reads the chip by close contact. Knowing where that spot is before you need it is worth a couple of minutes with the manual.

• Foot on the brake and the car in park or neutral.
• Fob inside the cabin and not blocked by metal or another electronic device.
• A healthy fob battery and a healthy car battery.
• A fob that the car has been taught to recognize.

Most smart keys carry a thin metal blade hidden inside the fob. A small release button or latch slides it out. The blade fits a mechanical lock in the driver door, which is often hidden behind a small cap on the outside handle. It exists for the day the fob battery is dead and the door will not unlock electronically.

The blade is almost always a basic design without electronics. It opens the door and sometimes the trunk or glove box. It does not start the engine. For that you need the fob to be read by the car, either by proximity or by the backup spot near the start button.

Few owners have ever used the blade, and many have never found the keyhole. Try it once, on a calm day. Pop the cap off the door handle gently, put the blade in, and see how it feels. If the lock is stiff or corroded, you want to know now. Our guide to key fob battery basics covers the matching maintenance steps.

A smart key runs on a small coin cell battery, and the signs of a dying battery build slowly. The range shortens, so you have to hold the fob nearer the door. The car starts complaining with a dash message about the key. The buttons need two presses. Most people notice and ignore it until the day it stops working completely, usually in a parking lot in the rain.

Changing the battery is a short job on most fobs. A small slot or latch opens the case, the coin cell comes out, and a new one goes in with the same orientation. The only skill involved is noticing which way the old one faced. Do it before the battery is dead, and keep a spare cell in the house, not in the car.

If you replace the battery and the fob still fails, the problem may be elsewhere. Water damage, a cracked circuit board, or a worn contact can all stop a fob from working. Try your spare. If the spare works, the first fob needs attention, and a locksmith can usually tell whether the case, the board or just the contacts have failed. If neither works, the car may have a problem that a key will not fix.

Losing a smart key is more serious than losing a plain one, because the fob is both a convenience and a security device. If it is lost at home, search carefully before panicking. If it is lost in a public place, consider that someone could find it and use it, since the fob works without a keyhole. Take that seriously if the vehicle is parked at your address.

A replacement fob has to be programmed to the vehicle. The work needs diagnostic equipment, and for many models it requires special security access to the car's system. It also lets the locksmith remove the lost fob from the list of accepted keys, so that a finder cannot use it. Ask about that step when you request the work.

If every fob is missing, the job takes longer, but it is a normal part of automotive locksmith work. You will need proof of ownership. Our car key replacement and key programming pages describe what is involved, and lost every key, what to gather lists what to bring.

A smart key can be locked in the car, but modern systems try to prevent it, and the warning chirps and door logic differ from one model to the next. Many cars will not lock when the fob is detected inside, or they chirp a warning. Some will lock anyway if a door is closed with the fob in a bag on the seat. When that happens, you cannot unlock by touch because the fob is on the wrong side of the door.

Do not force the door or try to wedge it open. Modern doors have airbags, wiring and electronics in them, and the weatherstripping is easy to damage. A locksmith opens vehicles with tools made for the job and with methods that avoid harm to the door. We do not describe the technique, but the aim is to leave no trace.

If you are stranded, our car lockout page explains the service. If a child or animal is inside, do not wait for any locksmith. Read the guide on a child or pet locked in a vehicle and call emergency services first.

The short range of a smart key is a security feature, but thieves have found ways to stretch it. A relay device can pick up the fob's signal near a house and boost it to a car in the driveway, fooling the car into thinking the fob is close. It does not break encryption, it simply extends the distance.

The simple defense is to keep the fob out of range of the doors when you are at home. A metal box, a signal blocking pouch or even a tin lined container can stop the signal. Some fobs have a sleep mode you can turn on by a particular button sequence, which the owner manual describes. None of this is complicated, and it removes the easy opportunity.

A second precaution is to park with some thought. A car in a well lit spot, with the steering wheel turned, in a garage if you have one, is a harder target. Whether your home is in town or out along a rural road, the principle is the same. Make the easy route a little harder.

Smart keys meet some of their hardest tests in this region. In summer, a fob left on a dashboard in the valley can be exposed to heat that shortens battery life and warps the case. In winter, mountain towns like Mount Shasta, Weed and McCloud bring cold that wears coin cells down sooner and makes plastic fragile. A fob that works all summer may give up on the first frosty morning.

Water is another hazard. Keys fall into rivers, lakes and creeks in this part of California, and a fob that has been under water is unreliable even after it dries. If it happens, remove the battery, let the fob dry thoroughly, and test it with care. If it fails, plan for a replacement and use your spare in the meantime.

Remote stretches of Interstate 5, Highway 299 and Highway 89 also make a dead fob a bigger problem. A long drive far from help turns a small annoyance into a real one. A spare key, kept somewhere other than the car, and a spare battery, kept at home, are the two habits that prevent that.

One myth is that a smart key makes the car easier to steal. The truth is mixed. Relay tricks exist, but the underlying encryption is stronger than the old plain metal key system, and a car that needs a registered fob is harder to start without one. The weak point is usually the owner leaving the fob near the door, not the technology itself.

Another myth is that you can simply buy any fob online and it will work. A fob must match the vehicle's frequency, its chip type and its security system. A low priced blank bought from an unknown seller may look right and fail at the programming step. Ask for the exact part type before buying, or let the locksmith source it so the whole job is one piece.

A third myth is that a dead fob means a dead car. It almost never does. Between the backup start spot, the hidden blade and a fresh coin cell, a stranded owner usually has a path forward. The trouble comes from not knowing the path exists. Spend ten minutes with the owner manual and the problem becomes a minor inconvenience.

Good planning is simple. Make a spare while you still have a working fob. Replace the battery on a schedule, before the car complains. Learn where your backup start spot is. Find the hidden blade and try the door lock. Keep your registration and an identity document where you can find them, because a locksmith will ask for them.

Think about what you would do if you were locked out or stranded. Would you know who to call? Do you have the make, model and year in your phone? Do you know whether your vehicle has a second fob at home? That small amount of preparation takes minutes and turns a bad day into an inconvenience.

When you need help, tell us the vehicle and where it is using the request form. Our team travels in a branded service van with key cutting and programming equipment, and we will explain what the job involves before we begin. For the broader range of vehicle work, see our automotive locksmith page.