@R_W: very interesting. Thanks for the pointer. A while back I was working on reverse engineering a wireless rain gauge (http://www.acurite.com/environment/rain-gauge/acurite-digital-rain-gauge-with-self-emptying-wireless-rain-collector-00875.html) which uses similar reed-based measurement, and it wirelessly transmits 433MHz signals to a display unit. The signal can be easily captured using a 433MHz RF receiver. I was never able to figure out how the signal is encoded. But anyways, it’s good to know the gauge without the wireless part exists and is very inexpensive. Unless if the click frequency is super high, I think it’s possible to just use a GPIO pin to poll the clicks.