I found this on the web.... The most common problem gas is hydrogen, which interferes with carbon monoxide. A method to reduce this cross sensitivity is to use a second sensing electrode underneath the first sensing electrode. The first sensing electrode responds to both carbon monoxide and hydrogen while the second sensing electrode responds only to the excess hydrogen that has gone past the first sensing electrode.
The full story can be found at.. http://www.product-search.co.uk/iet-pub.com/features/oct2000/alphasense-oak.shtml I think this might be a good way to sense hydrogen build up in the garage while charging your EV. If I find out additional info confirming this I'll let the list know. Maybe this could have prevented the Th!nk fire we talked about previously on the list. Rod
