On Friday, February 28, 2014 11:51:26 AM UTC-5, Kurt Ullman wrote:
In article ,

wrote:



On Fri, 28 Feb 2014 02:51:22 -0600, Dean Hoffman

" wrote:





Thieves have some gizmo that disables car alarms and unlocks

the doors. From CBS Chicago: http://tinyurl.com/mzx7shg



There are actually 2 paths these sort of things can exploit. I believe

this one just overloads the key fob receiver by sending all of the

available codes in a short period of time. The more insidious devices

crack into the "OnStar" (or similar) interface. That gives them even

more capability.



There is also a receiver thing that, when you hit the fob to lock it,

grabs the signal and the codes. Then clone it. Easy Peasy.


It's not easy at all. Not if it uses rolling pseudo
random codes like all the garage door openers use
today, which AFAIK is what they do use in cars. That technology
has existed for decades and you can't defeat it by just grabbing
a code. Having the current code just sent doesn't do any good,
because the next time the code gets sent it's completely different
from the one that was just sent. The transmitter and the receiver
are both on the same pseudo random rolling sequence and you can't
figure that out by just grabbing a code or two that is sent.