I've always double tapped when locking. I just replaced the fob battery after 3½ years. Indeed there was a message on the cluster.

edit - my fob is always within 10 - 15 feet of the car most of the time.

 

Now that I have seen MBz-Master's video (post #43) and the short video in post #47, I am satisfied what I've suspected is true... Both the old AND new Keyless Go fobs work the same way.

I bought my W212 E-Class with Keyless GO in March, 2018. I can now tell you that I have not had to replace the battery in the fob

-- for the last THREE YEARS --

...because I keep both fobs in my Master Bedroom, about 75 feet from the car in the garage. The back-up fob has been stored deactivated in a bedroom drawer the entire time. My primary (activated) key fob sits on the dresser top, next to my wallet, etc. The car sits in my garage, unlocked. Did I mention it's been 3 years........?

MBz-Master's video illustrates what I've maintained all along but people choose to ignore... that the key within range of the car makes the car query to establish (or deny) a handshake. The handshake is NOT initiated when you touch the door handle.

Even if you maintain that the new fob goes asleep after minutes, then there is no real need for 2-click deactivation. Yet it remains, hmmmmm.... If you are replacing fob batteries every few months and leave the fob in the car or nearby, then you know that the fob really doesn't sleep (completely).

 

Keep in mind, when you double click the fob, you are just disabling that fob, not any "feature." As you discovered, any other activated fob in range will keep the handshake with the car.

 

Does that mean that after double clicking which only disables the FOB, that if the car is left in a parking lot for example, and people walk by with their FOBs, assuming they are not deactivated, that my Mercedes will attempt to handshake with each of them?

If that is the case, then if you leave your Mercedes in an airport parking lot for 10 days to 2 weeks, when you return there is high probability that with all the attempted "hand shakes" your battery will be dead.

If this is the case is there a work around?

 

This is the only part of MBz's video that I question. I think (but cannot prove) that keyless go fobs are programmed with a unique signal code that will query only cars of the same brand that are programmed to respond, like a Mercedes will only respond to a Mercedes Key Fob. Likewise, a Lexus fob will not get a response from a Mercedes vehicle, etc.

This implies that the car is "awake" to receive signals, too. Which means if you always keep an activated fob within range of the car, the car will not trully go to sleep, either, draining the battery (both fob and car battery) as in the video example. Both MBs I've owned have some power going to the clock and the small fan in the inside rear-view mirror housing, the alarm system, other functions? etc. So the car is never completely dormant.

 

I really wish we had a member here (maybe an MB engineer) who understands how the keys work, the priority tree that defines what does what first interacting with the car, and the list of what functions remain awake in the car in one state of shut-down versus another state, or another. There has to be someone, because at the moment, it appears the only people who know are the relay car thiefs, and they are not talking.

Once again, we've drifted afield from the intent of the original post. But really, it seems that all these issues are related at some point.

 

I think the car will only respond to a valid signal from your fob. Receiving takes very little power whereas transmitting s signal takes several times as much. I've parked at the airport for a week and did not have any battery issues. If I leave it longer I park in a secure place and use standby mode. IMO the only time the car totally sleeps is when it is in standby mode.

 

Here is the guy Sr. Automotive Editor at "Popular Mechanics". He is also Master Auto Technician for Toyota, but it doesn't matter as Keyless Go works pretty much the same in most cars. He actually wrote that the system can detect the SmartKey at 40-50 feet away! He also confirms that your car wakes up to any SmartKey walking by... not only the key from your car.

 

People are forgetting that our keys don't work like most. You have to wake the system with a physical touch (or a proximity kick at the rear) before the handshake is attempted. No battery drain when keys walk by at an airport is the reason that "why doesn't this stupid car act like my Corvette, where all I do is walk up and it unlocks?"

 

IMO the keyless system is awake. One does not have to touch the car for it to do a handshake with a fob. As long as I have not put the fob to sleep with a double tap and I'm within range the car will respond to the fob.

 

How so? We're talking about the Keyless Go function. Not the buttons, which work differently. How can you know the car is responding to the Keyless Go function unless you touch a door handle, kick the trunk opener or press the Start button? I remind you the buttons work over a far greater distance than Keyless Go because they use a different system with different receiving antennas.

 

I believe that they use the same handshake. Press a fob button and the handshake protocol begins; touch a door handle or other sensor and the handshake protocol begins. In other words the car is always waiting to start the handshake protocol. The exception is standby mode.

 

You are entitled to believe that. But I point out that the handshake is very different in those cases. The button transmits, over a fairly long distance, all the information that the car needs to validate it's the right key. The process is initiated by receivers in the door handles. The Keyless Go handshake is very different. It happens only in close proximity and is managed by quite a few antennas in different locations in the car. They determine, by triangulation, that the key is close to the car and whether it's inside or outside. They're very different systems. Historically, they were different devices (a key fob and a Keyless Go card).

 

A proximity movement to open the hatch implies that the system is awake and ready to respond. If the system was indeed asleep, it wouldn't be able to detect the slight movement under the vehicle required to open the hatch. Many times the hatch was opened by the slight movement of a garden hose sliding slowly under the car. BTW the no button function works with the fob 6 feet away from the vehicle (out of arms reach).

 

The proximity sensor under the rear bumper talks to a dedicated control module, which initiates hand shaking just like the capacitive sensor in the door handle.

 

I think we know because we observe that key fob batteries are draining when the keys are stored within range of the car, WITHOUT anyone touching anything. At this point, I believe the only thing we know for sure is that the car is awake anytime the key fob is within distance, implying that the car answers and establishes a preliminary handshake, prior to touching the door handle. And the converse... when the fob is stored out of range, the car goes to sleep, and the new style fobs go to sleep too, after laying still. In the former scenario, the fob battery drains more (and maybe the main car battery, too), and in the latter scenario, the fob battery is preserved.

 

I believe that terminology and exactly what comprises the "system" is the issue. IMO all the sensors that feed the "keyless" function are part of the "system". You are separating component parts from the overall "system".

 

I’ve had several cars with keyless access or comfort access, or whatever it’s called. I’ve never had a car that unlocks as you walk up to it. Every one of them, you have to put your hand inside the door handle for it to unlock. Now on my Acura, it does light up when you get close, but that’s it.

 

I have posted that my (two-year old) fob battery that's kept in the car has essentially the same voltage as its twin that's kept in a junk drawer far from the car. In other words, my experience is that the fob battery does not drain since it times out if not jostled. (That it does time out is obvious. The car takes a few seconds to wake the fob via NFC unless you move the battery before pressing Start, in which case it starts instantly.)

But in any case, you're mixing apples and oranges. The most recent discussion is about whether the car's battery will drain in an airport parking lot because of the proximity of other fobs. These are different discussions.

 

Quite a few cars will unlock when you approach. Teslas do, for one. But even with your Acura, it knowing that you're near without having to touch the door means that the car is constantly searching for keys and is therefore subject to some battery drain from the controller that's doing the searching. MB doesn't know you're there until you touch the car or kick under the rear bumper. That avoids battery drain.

 

After activating standby mode, do you leave the ignition switched on?

 

No. Switching on the ignition deactivates standby mode. Just set it and leave and lock the car.

 

I think you mistake 3 different stages of the vehicle communication with its key. The first stage is when the key sends an encrypted signal for a handshake. Handshake doesn't lock or unlock the car and doesn't perform any physical action. Your car remains locked. At that point, your car has to confirm that you have the right (one-of-a-kind key). This communication is initiated by the key (not by the car), and apparently, it can happen as far as 50 feet away from the car. That's how thieves steal cars using the so-called "relay attack." Thieves don't intercept the frequency from your SmartKey, and they really don't care what it is; they simply extend it by the translator or repeater to open your car. But they don't really know what frequency or code it uses because it's encrypted... however, they don't need to know.

But there is more! The SmartKey actually keeps looking for a car... even if the car is not within a range. The SmartKey looks for your car tirelessly and constantly. The only good thing when your SmartKey is not within reach of your car - is your car stops the communication and can go to sleep. That's why the Smartkey battery has to be replaced a lot more often than the regular key, and you should keep it away from your car.

Interestingly, the "handshake" is the first line of defense against the Relay theft, and if the handshake didn't happen - then the car won't unlock... even if you approach the car with the right key from your car. The Keyless Go won't work. That's why the relay attacks won't work unless there was a 2-stage authentication, which is not the case on older cars, by the way.

The 2nd stage of communication is when you approach your car very close and touch the door handle; only then (when all the planets are aligned) the doors will unlock.

On the latest models, there is a 3rd stage. The car will not start... unless the SmartKey is communicating from the inside of the car's interior. The SmartKey keeps the communication even when the vehicle is started and driven. Try to remove your key outside the car while it's running, and the car will show a warning immediately: "Key is not recognized". Relay Attack won't work either, because even if you unlock the door - you won't be able to start it since the keyfob is not present inside the car.

All of the above was designed against the huge number of easy thefts, especially widespread in Europe.

The latest Mercedes and BMW SmartKeys (from 2019 -2020) are now equipped with a motion sensor - to solve some problems. If you lay the key and don't touch it - it will go to sleep after a few minutes until you move it again, which is a relief. But the problem - this sensor is so small, it can easily be activated, for example, by wind, AC blowing, someone walking by, or if someone moves a drawer.

The only way to stop communication with your car is by double-clicking the lock button.

 

There's a few MB TSBs regarding high parasitic draw due to CAN activity. We recently worked on a '18 GLA 250 in which the main battery would lose enough charge to make starting difficult (multiple attempts, weak crank) after a few days of sitting (3 or more).

Quick parasitic current measurement with car off after a few minutes only indicated a 10-20 mA draw, totally normal. Hooked up a DMM capable of recording and let it run for 5 hrs with car off and locked. Sure enough after 4 hrs there was a spike to 5 A indicating a something awoke (module/s). Spoke with a friend who indicating there's CAN monitoring function built into vehicle and it can be read with Xentry.

Sure enough, in Xentry we were able to see the interior CAN was active (not normal). This car already had the HERMES software updated and main battery replaced... all which started after mouse damage to engine harness that was replaced by dealer.

In this case, the car will need to go back to dealer and have a CAN bus recorder installed. The recorder logs all activity and is used to further diagnose why certain modules may be waking up. Definitely a complicated issue and unfortunately a lot of time to figure out.

 

I wonder if having nearby Mercedes with their key fobs out will awaken our cars and drain the batteries? I want my old CLK 209 back.

P.S. Everyone should get a Faraday cage keyfob holder anyway.