> It's funny how you can totally ignore the obvious, simple, solution...

Oh many's the time I've started off with a simple circuit, made it
more and more complicated and eventually come full circle back
to a simple solution

> http://petertodd.ca/persist/2007-01-21/moment-schematic.png

Thanks

> I put this circuit next to the spot and arc welders at my school
> while they were running... No activations. Looks the delay should
> be enough to filter out noise. I assume in your circuit you put the
> resistor and capacitor in there to do the same, but in hardware ?

Well originally I had just a large (390k) pull-down and 10k + switch
to Vcc. That worked but INT was not being pulled down hard enough
and was prone to false trigering. In my product the switch may be
closed for a fraction of a second or for several days. Although 10uA
isn't really a killer (permanently closed, 2800mAh capacity -> 31 years)
there was still the problem of noise immunity

Simply reducing the 390k would have pushed up consumption. 100k
would have given reasonable battery life, but still too high. Then I
thought of using a cap to store Vcc and dump into a low-value pull-
down as a pulse. That actually functions as a debounce filter (although
bounce is not an issue here and wasn't the intention of the mods) but
most importantly blocks DC if the switch is left closed

I daresay the 3M3 could be substantially increased, decreasing current
further, but there's little point really. At 1.6uA worst-case, that's still
many times the life of these batteries, almost 200 years

> Out of curiosity, what does your circuit do anyhow?

Can't say (yet), sorry. When it goes on the shelves I'll tell
 
> Judging by the alkaline batteries, I assume you aren't aiming for a 10
> year battery life. :)

See above. With the consumption it has now, smaller batteries could
be used (AAAA or coins) but they're relatively expensive compared
with AA

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