How Exactly do Keyless Cars Work?

While it used to be a novelty, most vehicles on the roads these days are ‘keyless cars’, but what exactly does this mean, and how does the fob connect to the car?

So, first and foremost, while they’re known as ‘keyless’, the fob that you get with your car is the key, it just doesn’t necessarily need to be inserted into the steering column in order to work (although some vehicles still require this).

They’re ‘keyless’ because they don’t have physical blade and teeth that need to ‘unlock’ a physical locking mechanism, but they do need to pair with the car using what’s called a ‘handshake’.

Remember, if you're having issues with your keys, fob, and unlocking/locking of your vehicle, it can often be an issue with the FOB or CAS (car access system). The ECU Pro offers an affordable mail-in BMW and MINI car access system (CAS) repair service along with key fob replacement.

The Core Components of a Keyless Car System

To understand how keyless cars work, you need to know the four main components involved:

1. The Key Fob (Smart Key)

The key fob is a small electronic device that contains:

• A microchip
  

• A unique encrypted ID code
  

• A low-power radio transmitter and receiver
  

This code is paired exclusively with your vehicle, making it extremely difficult to duplicate.

2. The Control Module (Car Computer)

As for the car itself, it includes the control module which:

• Verifies the key’s encrypted code
  

• Confirms proximity
  

• Authorizes unlocking or engine start
  

If the signal checks out, the system grants access instantly.

How Keyless Entry Works Step by Step

Here’s what happens when you walk up to a keyless car:

1. Car sends a low-frequency signal
   

• The vehicle emits a short-range signal searching for its paired key fob.
  

2. Key fob responds
   

• If the key is within range (usually 3–5 feet), it replies with an encrypted radio signal.
  

3. System verifies the code
   

• The car compares the response with its stored ID.
  

4. Doors unlock automatically
   

• Touching the door handle triggers unlocking.
  

How Keyless Ignition (Push-Button Start) Works

Starting a keyless car is a separate but related process:

1. The car checks for the key fob inside the cabin
   

2. The system confirms the encrypted signal
   

3. The immobilizer disengages
   

4. Pressing the button starts the engine
   

If the key fob isn’t inside, the engine won’t start even if the doors are unlocked earlier.

And as mentioned earlier, there are two types of frequencies for keyless cars: active and passive. Some vehicles require the fob to be put into a slot on the column, which uses a single-frequency induction to start the car (passive). The other is a dual-frequency “handshake”, that uses a stronger frequency to start the car, even if the key is in your pocket, a cup holder, etc (active). To perform an active start, the fob needs to be able to transmit a higher frequency (315/433 MHz), whereas the passive start only needs a 125 kHz frequency, powered via induction (using the coil in the fob, just like an old non-remote key.

This offers convenience by eliminating physical keys, but this convenience comes with security risks like "relay theft," where thieves capture the fob's signal to gain access.

How do BMW and MINI CAS mail-in repairs work?

When you're having issues with your keys, fob, and unlocking/locking of your vehicle, it can often be an issue with the CAS (car access system).

The ECU Pro offers an affordable mail-in BMW and MINI car access system (CAS) repair service. To have your CAS repaired, simply remove the CAS and mail it to us. Our professional team will either test, repair, or clone your unit.