cetialpha5

It's called a Faraday cage. There's all different types on Amazon. This one for under $10 even has a picture of an MB key in it.

DFWdude

Speaking of Faraday cages, I have been experimenting with these myself. First attempt was a small breed dog feeding bowl (Aluminum), with a lid made of aluminum foil wrapped around a pickle jar lid. The wrapped lid sits down inside the sloped wall of the dog bowl, finding a place where it seals the lid to the bowl. I found this VERY necessary, because any tiny gap where the parts meet allows the signal to exit. Testing FAIL.

For this reason, I doubt that the fold-over pouch type found on Amazon will work as the fold doesn’t seal perfectly.

My second experiment works perfectly. I shopped a resale store for an aluminum cup with a sealing aluminum lid. I had to buy two items, one the cup, and a second jar (glass) with an aluminum lid. Altogether, I spent $1.60 for both items. Sit the glass jar aside.




The aluminum lid from the glass jar nests into the cup perfectly (albeit upside-down), and the sealing edge of the lid is deep enough to seal both parts together without fail.

In use, I can lock the car, then place the key within the cup, install the lid, and sit it on the ground 2 feet from the car door. After repeated attempts, the car will NOT unlock when I insert my hand through the door handle.

Once satisfied that it worked, I then added some colorful padding within the cup to eliminate key rubbing on the hard aluminum interior. And I super-glued a plastic bottle cap to the lid to provide a grip to pull the lid out of the cup.



The completed faraday cup sits on my dresser inside a walk-in closet, 75 feet from the car in the garage. It takes hardly any room at all. And even though I live in an area that hasn't seen any crime in decades, no one driving by can hijack the signal from the key and relay it to the car. Not that they can open the garage door to get at the car anyways.

ghlkal

I had not heard this before.

I need to try and see if this works with an older fob like mine (2012)

Tuxdude

It usually lights up the red indicator on the fob a little longer when that works. I'm not entirely sure starting which year and which models they started doing this. It's part of most recent (2-3 years) keyfobs at least.

KEY08

My 2014 functions that way. Yes the LED will pause when flashing to let you know it is engaged.

DFWdude

The key fobs for my 2001 C-Class work this way to turn them off. So this is not new.

diesel_dan

On our 2013 with Keyless Go we were mowing through FOB batteries when we left them with all our other keys in a kitchen drawer, 10 or so feet from the car.

We moved both FOBs to a drawer in our Master and the battery life has notably improved - probably 25-30 feet away now. I think I might put a small tin can in the drawer, or line it with foil, now that I've been reading this thread... I do believe the keys are continuously trying to keep in contact with the car if they are within range.

kajtek1

I tried double close click on my 2014 model.
No kudos - the door will still open with hand pull.

cetialpha5

I've tried many different brands, Energizer, Sony, Duracell, Panasonic, they all lasted about the same amount of time. The energizers tended to have the highest starting voltage. I believe they're Panasonic from the dealer. Doesn't seem to make a difference. Going to stick with Energizers.

Arrie

Same with my 2010.

Sunnyslope48

Same with my 2016 E350. My manual says double click will turn it off, but I guuss my car didn't read the manual like I did.

chassis

On my W166 I received the "key not detected" message in the MFD. I replaced the fob battery and all good. The fob battery was one year old.

kajtek1

So what I understand from the system and correct me if I am wrong.
-key sends pings all the time and usually batteries last over a year
-there is no motion switch in the key.
-you can screen the key to prevent car theft, but that will have no effect on battery life
- pressing the button has to shorten the battery life, but that might be hard to estimate by how much.

So for those complains about short battery live, could it be they press the buttons often, or keep the button pressed in their pocket?

cetialpha5

Interesting theory about the button being pressed. I would say no though. I don't press the buttons and of course I wouldn't know if the buttons were pressed while in my pocket. However I have two sets of keys for two cars so 4 fobs and when I replace the batteries in the one I use everyday, I also have to replace the batteries in the fobs that just sit at home. Both sets die at about the same time and I measure the voltage and they're pretty close to each other even though one set gets constant use and the other one just sits around in the drawer at home.

ghlkal

Yup, my 2012 fob doesn't turn off with a double lock press either.

Tuxdude

You're missing the fact that you can increase your battery life and also prevent car theft by pressing lock twice (if it is supported in your keyfob), which stops the keyfob from sending pings. If your keyfob supports this option, this technique is way better than screening the key using any foils or faraday cages. Certain newer keyfobs (For example in my 2019 C63S) stops the pings automatically after two minutes of being idle (without any physical movement).

chuang

By using CR2032 (thicker) would it damage the keyfob housing in the long run? Thoughts? Thanks!

thenew3

I don't think so. At least it hasn't in the nearly 7 years I've been doing it.

Arrie

I have used 2032 for almost 8 years with no problems.

DFWdude

The double click works to deactivate Keyless-Go on my 2016 E350, manufactured July 20, 2015

I can't fit a CR2032 battery into my fob for all the tea in China.

On balance, I'll take the first statement before the second any day.