Re: Fail-safe for keyless entry

[Ian Shef <invalid@xxxxxxxxxxxxx>]

"Robert Green" <robert_green1963@xxxxxxxxx> wrote in
news:hqi2ge$6a7$1@xxxxxxxxxxxxxxxxx:

> I've got the typical minivan keyless entry keychain fob but it's got a
> serious design problem.
<snip>
> The real estate inside the fob is very cramped.  It runs off a CR2032
> coin cell battery, and the circuit traces are simple enough so that I
> could scrape off the 3VDC+ line and bridge it with a small switch.  That
> way, I could just put in a tiny pushbutton that had to be depressed as
> well as the desired command button each time a command was sent.  That
> approach makes it a two-handed operation, whereas a slide type ON/OFF
> switch could still be worked with one hand.

Before you scrape circuit traces or install switches, please try a simple
experiment:

Remove the battery for a few hours (as if you had turned off the switch),
then reinstall the battery and see what it takes to unlock your minivan.

Many keyless entry fobs use a trickle of battery current to maintain state
information (such as where they are in a rolling code).  The system can
reacquire the state, but it may take multiple presses.  Furthermore, since
the state after power-off/power-on is likely to be the same each time (for
the same fob under similar conditions), you may be defeating the purpose of
the rolling code.

I may be wrong, but the experiment is a lot easier than all of the wasted
work if I am right.


Good luck!

<snip>