2021 CX-5 Key Battery Low
- Thread starter msalvetti
- Start date
I'm using Duracell 2025s.
Okay, thanks, I'll replace the 2025s with 2032s and see what happens.
BTW, the spare key fob started acting up too.
Got a message yesterday that my battery was low and that I should hold the fob close to the Start button.
The remote lock/open key fob is still working...
MrViking
2022 CX5 Premium
As I understand it, the car puts out a low frequency signal that creates a field around it that is not very strong. It's on all the time and the car battery can power it for a long time. When your fob gets within this range, it activates and communicates (exchanges data and codes) with the car and allows you to unlock, start it, etc. When you leave this small field, your fob turns off and no longer communicates with the vehicle. This is how your CX-5 can be set to auto-lock when you walk away. You leave the field and the car knows it and locks. The way thieves thwart this technology is by being within that low frequency field with a a sophisticated electronic monitoring device that picks up that low frequency signal and then amplifies/retransmits it thus increasing that low frequency field enough to activate your key fob in the house and the fob and car being their data exchange. The bad actor partner, closer to the house then captures the communication between the key fob and what it thinks is the car. The bad actor is then able to replicate your fob to open and start the car. So keep you car in the garage where the thief and his gear can't get close enough to be within the low frequency field and as others have recommended, get a Faraday pouch or box which isolates whatever is in it, like your fob, from bogus radio transmissions.
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N7turbo
2023 CX-5 2.5T ... 2024 MX-5 RF GT
But I can unlock the car from 100 feet away, so I don't think this is on all the time. The only time this activates, as far as I can tell, is when the unlock button is pressed and the car is "armed" for a time. Then it will check for the fob nearby before allowing ignition. It also stays on continuously as long as the engine is running. We know this is true because if you leave the car while it's running, it will beep at you. So maybe the folks with battery drain issues are just spending more time in the car. That makes sense because at only 5K miles/year, my batteries last 2-3 years.
MrViking
2022 CX5 Premium
Remember that when you push any of the buttons, that's a different frequency at higher power than what is used for the car to recognize that you're near it and allows all those remote functions like push-button start and auto lock when walking away. Also, the push-button start can use NFC (Near Field Communications) to start so the push-button start will work with a totally or even no battery in the fob.
I've postulated the same thing that the longer you're inside the car, the faster the fob battery will drain as that system in the fob stays active. It makes sense but I don't know for sure.
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- 2016.5 CX-5 GT AWD titanium/black 2016 Miata Club ST MT white
How does the faraday box prevent the fob from draining?
If you're thinking that the fob transmits all the time, I believe that you're wrong. From an engineering standpoint it wouldn't make sense. BUT, if that is the case, how does the bag prevent the fob from transmitting? Is doesn't and it can't. If the fob transmits all the time, it will be more than happy to transmit inside the box, even if the signals aren't going anywhere.
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- 2016.5 CX-5 GT AWD titanium/black 2016 Miata Club ST MT white
If this was the case, then there would be no need to press action buttons on the car or the fob. You would be able to just walk up to the car and open the door.
"the car puts out a low frequency signal that creates a field around it that is not very strong."
What would be the purpose of this 'low frequency signal'? Yes, I see what you said above, and it doesn't make sense.
Rather than always transmitting these things are always listening, both the car and the fob. It takes considerably less power to listen than it does to constantly transmit.
When you walk up to your car and press the action button to open a door, the car sends out a signal and the fob is listening for this. If all is well, the fob returns a signal, a handshake, and now the door can be unlocked and opened. If you walk up to the car and press the fob button instead of the car's action button, the fob sends out a signal that the car is waiting for, again, if all is well, the car unlocks.
"The way thieves thwart this technology is by being within that low frequency field with a a sophisticated electronic monitoring device that picks up that low frequency signal and then amplifies/retransmits it thus increasing that low frequency field enough to activate your key fob in the house and the fob and car being their data exchange. "
This is exactly why there is no 'low frequency field' generated. No reason to have this at all especially when thieves can do what you suggested above. Why make it easier for them?
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- 2016.5 CX-5 GT AWD titanium/black 2016 Miata Club ST MT white
No, I'm sorry, it doesn't make any sense.
MrViking
2022 CX5 Premium
Your are correct in that the fob does not transmit all the time. It's only active when in the small perimeter around the vehicle. Even then I doubt it's transmitting all the time although it may be in a low power listening mode.
MrViking
2022 CX5 Premium
To me, once the fob gets within the low frequency perimeter of the vehicle, it's active and thus using battery. The longer in that zone, the longer the fob is active and the more battery it uses. Also, we need to understand the difference between being active (on) and transmitting. Simply being on uses very little power. Transmitting will use much more power, especially using the buttons as the signal needs to be more powerful to go the longer distances.
It's quite sophisticated as the car also has to differentiate between the fob being inside or outside the vehicle.
MrViking
2022 CX5 Premium
Your car detects that the key fob is close by using a technology called radio-frequency identification (RFID) or low-frequency (LF) communication combined with higher-frequency signals. Here's how it works:
1. Proximity Sensors in the Car
The car is equipped with proximity sensors near the doors and inside the cabin. These sensors emit a low-frequency signal (typically 125 kHz or similar) to "search" for the key fob.
2. Key Fob Responds
When the key fob is within range of the car's low-frequency signal, it responds by transmitting a unique, encrypted signal back to the car. This response typically occurs over a higher-frequency radio signal (e.g., 315 MHz or 433 MHz).
3. Authentication
The car verifies the key fob's signal by matching it to a code stored in the car's computer system.
If the code matches, the car unlocks or allows the engine to start.
4. Interior Detection
Once inside the car, additional sensors verify that the key fob is inside the cabin (not just near the car). This ensures the car won’t start if the key fob is outside, such as in your pocket while standing next to the vehicle.
5. Push-Button Start
For push-button start systems, the car checks for the key fob’s presence before enabling the ignition system.
Range of Detection
Proximity detection range for keyless entry is usually about 1-2 meters (3-6 feet) around the car.
For push-button start, the key fob must typically be within the car's interior.
Security Measures
Modern key fobs use rolling codes or encrypted communication to prevent replay attacks.
Some systems use ultra-wideband (UWB) technology for even more secure and precise location tracking.
By combining these technologies, the car ensures that only an authorized key fob within close proximity can unlock or start the vehicle.
Hope this helps.
MrViking
2022 CX5 Premium
Thieves can start a car while the key fob is inside your house using a technique known as a relay attack or other similar exploits. Here's how it typically works:
1. Relay Attack
What Happens:
Thieves use two devices: one near your house (close to where the key fob is located) and the other near your car. The first device captures the low-frequency signal from your car and relays it to the second device near the key fob inside your house. The key fob responds as if it's close to the car, and the signal is relayed back to the car, tricking it into unlocking and starting.
How It Works:
The car thinks the key fob is nearby because the relay devices extend the communication range artificially.
2. Signal Amplification
What Happens:
A specialized device amplifies the weak signal emitted by the key fob, making it detectable by the car even at a greater distance.The car unlocks and starts because it believes the key is within range.
3. Key Programming
What Happens:
Thieves gain access to the car's interior (e.g., by breaking in or using a signal jammer).
Using a device connected to the car’s On-Board Diagnostics (OBD) port, they program a new key fob for the car. The newly programmed key allows them to start the vehicle.
4. Signal Cloning
What Happens:
If thieves capture the key fob’s signal while you lock or unlock the car (using a device called a code grabber), they can replicate it. This allows them to unlock and start the car later.
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- 2022 CX-5 Turbo
Prevent fob battery drain: Where I place my fobs is not that far from my garage. I obviously have no data to show that this matters. Feel free to question it. I know how PKE (Passive Keyless Entry) works.
Relay Theft: With my fob in a Faraday box near the door, I cannot even open the door. Tested. Believe it or not, I tested with a metal cookie box. I still could open the doors in 1 of 5 attempts. Not 100%.
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- 2014 & 2019 CX-5 Touring(s)
Heh, I tried the same with an Altoids tin. I was surprised, but it didn't block the signal either.
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- 2016.5 CX-5 GT AWD titanium/black 2016 Miata Club ST MT white
Did you read post #28?
Where are you getting your info, especially the part about the low-freq signal that you believe is being generated by the car 24/7?
What would be the purpose of this, compared to how I said the system operates? Having this low-freq signal always on would be a security risk, again, why do you think this is the case?
You're mostly close above but not quite. So, no, it doesn't help. I've been working with and on electronics for over 35 years and I do know a little bit about the subject.
MrViking
2022 CX5 Premium
Yes, I did read thread 28 and what I've posted previously seems to answer the questions asked. My CX-5 is the third vehicle that I've had with keyless entry. When I got my first one, I was really curious on how it worked. How did it know that the key fob was near so the door would unlock when I pushed the button? How did the car know if the fob was inside or outside? Even in the trunk as the it wouldn't latch if the fob was in a purse or coat pocket. How can the push button start work even if there's no batter in the fob? So I researched it and read a number of articles unit I understood it. What I posted is what I've learned and it all makes sense to me. So I'm just sharing what I've learned for those who want to understand it. If it doesn't work the way I've posted, I'd be very interested in the links of sites that explain it differently.
With all that said,I have no interest in disputing about it. If someone thinks/believes it works differently, that's fine. If I'm wrong, I'd really like to understand it accurately.
Just an FYI - I do have a degree in electronics although I don't work in that industry directly.
With all that said,I have no interest in disputing about it. If someone thinks/believes it works differently, that's fine. If I'm wrong, I'd really like to understand it accurately.
Just an FYI - I do have a degree in electronics although I don't work in that industry directly.
N7turbo
2023 CX-5 2.5T ... 2024 MX-5 RF GT
It doesn't answer the question when do these antennas activate.
Are they always on, or do they send/receive only once a button is pressed? The latter makes a lot more sense to me.
MrViking
2022 CX5 Premium
Yes, they are always transmitting the low frequency field seen in the diagram. When a key fob enters the field, an encrypted exchange between fob and car begins to determine if the fob is one that is stored in the computer. (I think the computer can store up to four) If it is, the door can be unlocked and the car started once it enters the interior of the vehicle.
The fob (while it can vary depending on the system) is typically in a low-power state so that it can determine when it enters a vehicle's keyless entry zone. This is why a Faraday box is necessary for the fob as the bad actors can extend the range of the vehicle's keyless entry zone and trick the fob into beginning the exchange. The Faraday box will block the low-power signal from the fob and also prevent the signal from the vehicle from reaching it. A Faraday box is better than some kind of metal can or box as both the material and size of the mesh are critical in the range of frequencies that are blocked. Faraday cages are designed to block radio waves. Metal boxes are not.
The fob (while it can vary depending on the system) is typically in a low-power state so that it can determine when it enters a vehicle's keyless entry zone. This is why a Faraday box is necessary for the fob as the bad actors can extend the range of the vehicle's keyless entry zone and trick the fob into beginning the exchange. The Faraday box will block the low-power signal from the fob and also prevent the signal from the vehicle from reaching it. A Faraday box is better than some kind of metal can or box as both the material and size of the mesh are critical in the range of frequencies that are blocked. Faraday cages are designed to block radio waves. Metal boxes are not.
