How Does Keyless Entry Work on Cars? | The Tech Explained Simply

The technology behind keyless entry is simpler than the name suggests. Your key fob transmits a unique, encrypted wireless signal, and the car checks that code against what it has stored. If they match, the doors unlock. On most modern vehicles, this same authentication happens again inside the cabin before the engine will start.

Understanding whether you have a passive proximity system or a button-press remote changes how you use it, what range to expect, and how to keep your car secure. This guide breaks down the mechanics, the two main system types, and the common pitfalls that trip up drivers.

What Are The Two Main Types Of Keyless Entry?

Nearly every car sold in the U.S. today includes some form of keyless entry, but the technology comes in two distinct flavors. Knowing which one you have is the first step to using it correctly.

Active Remote Keyless Entry (RKE): This is the classic key fob with buttons. You press “unlock” or “lock,” the fob transmits a coded command, and the car’s receiver actuates the door locks if the code checks out. You are actively initiating the action.

Passive Keyless Entry (PKE): This is what most people think of as “smart key” or “proximity” entry. With passive systems, you don’t touch the fob at all. The car emits a low-frequency signal to check for the key’s presence. When you pull the door handle, the system wakes up the fob, which sends back an authenticated response over a radio channel. If the response is valid and the key is within the short-range detection zone, the door unlocks automatically. Mercedes-Benz brands this as Keyless-Go, and KBB commonly calls these proximity keys.

What Frequencies And Hardware Make It Work?

The system relies on two different types of radio communication to balance range and security. The key fob and the car are constantly, or near-constantly, talking to each other in a way that is both convenient and difficult to spoof.

• Short-range proximity (LF): Passive entry uses a low-frequency signal, typically at 125 kHz or 134.2 kHz, for the initial challenge. This signal is weak by design, which confines the detection zone to just a few feet around the car’s antennas.
• Command transmission (RF): Once woken up, the fob replies over a radio frequency band—commonly 315 MHz or 433 MHz in the U.S., depending on the manufacturer’s implementation.
• Vehicle hardware: The system depends on several antennas placed around the car, a central receiver module, and the body control module (BCM). These components work with the immobilizer ECU to confirm the key is not just close to the car but actually inside it before enabling push-button start.

Typical Range And How To Use It

Forgetting the range limits of your system is a common mistake. Remote keyless entry fobs typically work from a few feet up to about 5–20 meters (16–66 feet), but the passive proximity detection for door unlocking requires you to be essentially next to the vehicle.

Here is the common operation sequence for a passive entry system:

1. Approach the car with the paired key fob in your pocket or bag.
2. Touch or pull the door handle. The car’s antenna sends a low-frequency challenge to wake the fob.
3. The fob transmits its encrypted response back over the RF channel.
4. The vehicle verifies the code and unlocks the door. Once inside, a separate check confirms the key is in the cabin before pressing the start button.

If you are in the market for a new vehicle, this technology can vary significantly by brand and trim level. Some cars unlock when you touch the handle, others do it automatically as you approach. Reviewing the best vehicle keyless entry systems can help you decide which features actually matter for your next purchase.

Are There Security Risks With Keyless Entry?

The convenience of keyless entry comes with a known vulnerability. Passive systems can be susceptible to “relay attacks,” where two attackers use specialized equipment to extend the key’s signal range. By placing one device near your front door to amplify the fob’s signal to another device near the car, they can trick the vehicle into thinking the key is right next to it, allowing them to unlock and even drive away.

Basic precautions greatly reduce this risk. Keep your keys away from exterior walls and entrances, ideally in a metal tin or an RFID-blocking pouch when you’re not driving. Also, remember that a coded fob is only compatible with the specific car it was paired to; a replacement key must match your vehicle’s stored credentials, which usually requires dealer or locksmith programming.