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Discussion Starter #1
Several folks at our Honda dealer warned us about letting our keyless fobs get too close to each other. One said that if the fobs get with roughly 30" or so from each other, they will "talk to each other" and this will then reduce the battery life of each fob. Another said that this was wrong. He explained that if the two fobs are INSIDE the car at the same time, the car sees both and this causes confusion about which fob the car should read for desired seat position, etc. Then he said that this causes a continuous three-way "chat" as the car hops back and forth between the fobs, again, leading to excessive fob battery usage and shorter fob battery life.

Since my wife and I are in the habit of carrying spare car keys, needless to say all the above came as unwelcome information (especially if we are on a road trip where the two fobs would be simultaneously inside the car for a long time). So taking them at their word, we tried shielding one of the fobs, but this did not work. Amazingly, whether a metal can, aluminum foil, or whatever else we tried as a shield, the car could still see the "shielded" fob.

Does any of the above make sense and sound like a real problem? If yes, I'd call this very poor engineering, but maybe the dealership personnel have this all wrong. Any thoughts....?

John
 

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Discussion Starter #3
That's true, but I would still like to know how one or more FOBs interact with the car. For instance, is the car constantly sending our a signal "looking" for a nearby FOB? Or is it the reverse and the FOB is constantly looking for a car? I assume the former, but who knows. And when two FOBS are simultaneously in the car, or does the car "see" both of them, just one (I suppose the one closest to the Start switch)? In other words, as is said in engineering, I'd like to know the handshake sequence used between the FOB and the car. There are two reasons for my quest:

1) As said earlier, the impact on the FOB batteries.

2) However more recently there have been odd car break-ins in our neighborhood. Ones where the cars were locked, but there is no sign of forced entry, and no obvious use of a slim-jim. This has grown into a huge discussion on our neighborhood forum. One idea floated by both neighbors and police is that there is now available some kind of FOB interceptor / amplifier for use by theives. No one seems to have specifics, but the claim is that it's some small box which scans for the signal(s) from the car and/or the FOB, and then the signal(s) are amplified such that the car doors become unlocked. They have said that the receiver in this box is sensitive enough to pick up the signal(s) from quite a distance (like from within your home). At first I thought this might be urban myth, but when officers in our local PD brought it up, it made me even more curious on EXACTLY how these keyless entry systems work (in my case, in a 2015 model CR-V).
 

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Discussion Starter #5
Interesting write up from Snopes.com
Link: http://www.snopes.com/autos/techno/lockcode.asp

You will have to read it to the end.
I read the whole thing. It sounds like shielding the FOB when it isn't needed might be a good plan (the only exception being whether the rolling code scheme Honda now uses might make the shielding unnecessary). There are shielded bags available, and I found several kinds of shielding "fabric" on Amazon. One of these fabrics shows over 80 dB of attenuation at the frequency used by the FOB. I have sent the seller a query about whether this stuff can be sewn using conventional techniques -- so far, no reply. :-(
 

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My guess is that the first one to approach the vehicle and make a connection will be the one it talks with for that 'driving session'. I had 4 of them in one of our 2015's the other day, and had no problems.

Now if you walk a few steps away from the car with it, while the motor is running, it complains loudly :)

Rhody
 

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Discussion Starter #7
My guess is that the first one to approach the vehicle and make a connection will be the one it talks with for that 'driving session'. I had 4 of them in one of our 2015's the other day, and had no problems.

Now if you walk a few steps away from the car with it, while the motor is running, it complains loudly :)

Rhody
There are several aspects to this key less entry topic -- multiple fobs in the car at the same time, thieves using jammers, thieves using repeater amplifiers, etc. There seems to be little written in the public domain on all this (understandable -- the stuff needs to be treated as classified), but it seems that the latest Honda rolling code systems ~may~ be rated pretty well against intrusion. However since so much of this is anecdotal, I've decided to just punt and build some shielded bags -- Faraday cages of sorts. Turns out there is some excellent shielded material for this sold on Amazon.com. It goes by the name of Cobaltex. Assuming the Honda system operates at around 400-450 MHz (like many other foreign brands), this material provides around 100 dB of attenuation for electric fields, and maybe 70-80 dB for magnetic fields. And this is for just one layer of the fabric. A sheet of the stuff is around $25 with shipping, but it's 4 ft x 1 ft in size, enough to make multiple covers/bags. I have also found some pre-made shield bags at $30 each, but with no specs -- not even their size, thus the home project.
 
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