Poul-Henning Kamp wants to track his natural gas usage. He knows that his meter has an impulse output port, but it is hidden inside the sealed meter. I know this wouldn’t stop a lot of our readers from figuring out how to use it, but he has a very clever, non-obtrusive solution, to the problem.

A closer examination of the gas meter showed no signs of where the built-in impulse output were located, leading me to conclude that it probably is somewhere inside the sealed section of the meter where it would get me in legal trouble, not to mention potential explosion hazard to fiddle with it.

But I did notice something else: it is implemented optically rather than mechanically because the zero on the least significant digit is a shiny metallic oval rather than a painted white numeral.

How to monitor your gas meter –Link