Remote keyless entry (RKE) is a system that lets you lock and unlock your car by pressing a button on a small handheld transmitter, commonly called a key fob. Instead of physically inserting a key into the door lock, the fob sends a radio signal to your car’s onboard computer, which activates the door locks. Nearly every car sold today includes some form of this technology, and it has been standard equipment since the late 1990s.
How the Signal Works
When you press a button on your key fob, a tiny transmitter inside sends a coded radio frequency signal to a receiver in your car. In the United States, these signals operate at 315 MHz. The fob and the car’s controller chip share a matched algorithm that generates a 40-bit code. The car’s receiver runs the same algorithm to produce the same code, and if the two match, the command goes through: doors lock, unlock, or the trunk pops open.
This entire exchange happens in a fraction of a second and works from roughly 30 to 60 feet away, depending on the vehicle and conditions. The fob is powered by a small coin-cell battery (usually a CR2032) that typically lasts two to four years with normal use, meaning a few lock and unlock cycles per day.
Rolling Codes Prevent Signal Theft
Early keyless entry systems used a fixed code, which meant a thief with the right equipment could record your signal and replay it later to unlock your car. Modern systems solve this with rolling codes, sometimes called hopping codes. Every time you press the button, a counter value inside the fob increases, and a new encrypted code is generated. The car decrypts the signal, checks that the counter value falls within an expected window above the last accepted value, and only then executes the command. Once a code has been received, it’s permanently invalid.
This means recording a single transmission is useless to an attacker because the code will never work a second time. A widely used encryption method for this process is the Keeloq block cipher, which scrambles the rolling code so that even intercepting multiple transmissions doesn’t reveal the pattern needed to predict the next valid code. The “window” of accepted counter values also accounts for real-world use. If you accidentally press the button several times while out of range, the car still accepts the next signal because it allows a range of counter values, not just the very next one.
RKE vs. Passive Keyless Entry
Remote keyless entry requires you to press a button. Passive keyless entry (PKE), sometimes branded as “Keyless Go” or “Comfort Access,” works differently: your key fob stays in your pocket, and the car detects it automatically when you approach. You unlock the door by touching the handle and start the engine with a push button, all without ever pulling out the fob.
PKE systems use a low-frequency signal from the car to “wake up” the fob when it’s within a few feet, then the fob responds with its authentication code. This is more convenient but introduces a specific security vulnerability that standard button-press RKE systems don’t share as easily.
Relay Attacks and How to Guard Against Them
The main security risk with passive keyless systems is the relay attack. It works like this: two thieves coordinate, one standing near your car and the other near your home. The person near your house uses a device that picks up the weak signal from your key fob, even through walls, from distances up to 100 meters. That signal is relayed to the second device near your car, which tricks the vehicle into thinking the fob is right next to it. The doors unlock, the thieves get in, and the engine starts normally. The whole process takes seconds.
Standard button-press RKE fobs are less vulnerable to this because they don’t broadcast a signal unless you physically press a button. If your car uses passive keyless entry, a few practical steps reduce the risk. Storing your fob in a signal-blocking pouch (often called a Faraday pouch) prevents the signal from being picked up through your walls. Some newer fobs include motion sensors that put the fob to sleep after a period of stillness, so a fob sitting on your kitchen counter won’t respond to a relay device. Keeping your fob away from doors and windows also reduces the chance a relay device can reach it.
Smartphone-Based Car Keys
The latest evolution moves the key fob’s job to your smartphone. These systems rely on three wireless technologies working together. Bluetooth Low Energy (BLE) detects your phone from about 30 meters away and begins an initial authentication exchange. Ultra-Wideband (UWB) then takes over for precise positioning, pinpointing exactly where the phone is relative to the car, even distinguishing whether you’re inside or outside the vehicle. Near Field Communication (NFC) serves as a backup, requiring you to hold your phone against the door handle, useful when your phone’s battery is low.
The combination of BLE and UWB enables fully passive, hands-free access similar to a passive key fob, but with a significant security advantage. UWB measures the actual physical distance between the phone and the car with high accuracy, which makes relay attacks far more difficult because the system can tell the difference between a phone that’s genuinely nearby and a relayed signal pretending to be. Several automakers now offer phone-as-key systems, and the technology is expected to become widespread as more phones ship with UWB hardware.
A Brief History
The first production car with a handheld remote keyless entry transmitter was the Renault Fuego in 1982. By 1983, several American Motors vehicles offered it as an option, including the Renault Alliance. Through the late 1980s and 1990s, the technology spread across manufacturers and price points, moving from a luxury add-on to a near-universal feature. Today, even base-model vehicles typically include at least a basic RKE fob.
Replacing a Key Fob Battery
When your fob’s range starts shrinking or it takes multiple presses to get a response, the battery is likely dying. Most fobs use a CR2032 lithium coin cell that costs a few dollars and can be swapped at home in under a minute. You’ll typically pry open the fob’s plastic case with a small flathead screwdriver or a coin, pop out the old battery, and press in the new one with the correct side facing up. No reprogramming is needed for a simple battery swap, as the fob retains its pairing with your car. If you lose a fob entirely or need a spare, replacement and programming through a dealer or locksmith is significantly more expensive, often ranging from $100 to $400 depending on the vehicle.