Re: [Discuss-gnuradio] Car alarms and garage door openers

[Marcus Leech]

Matt Ettus wrote:
> After the Wired article today, I've received a couple of email from 
> people who are concerned that the USRP could be used to clone their 
> keyfob transmitters for car alarms and garage doors.  I'm not 
> concerned, since there are already many ways to do this (just check 
> the back of pupular science magazine).  However, I am curious about 
> it.  I know that we can capture and play back any rf signal.  The 
> question is whether that replayed signal would result in the door 
> being unlocked.  I was under the impression that most of those systems 
> allow an unlock code to only be used once, but does anyone out there 
> know for sure?
>
> Matt
Most, but not all, such devices now use a "rotating code sequence", 
based on a not-very-long pseudo-random sequence.
 Certainly for the impatient burglar, merely replaying won't work in 
most cases.  I don't know how they maintain
 synchronization between the key and the lock, and it's likely that 
there are weaknesses there.