With the code mostly complete, I can try actually running this at night and seeing how much water is remaining when the alarm goes off. The water usually doesn't run out during a 6-7 hour of sleep, so I'll need to fill it up half-way or so to ensure the water will run dry.
The hanger is the main input for this device. While on the hanger, the device sits waiting for an input, but once removed from the hanger, the measurements begin. Calibration and alarm test can only be done with the mask on the hanger.
The hanger is very hacked together. I will eventually find a better, more elegant way to implement this. The push button was chosen through Digikey's search system with priority on the amount of force required to depress the button. The mask is quite light, so the button needed to be very sensitive.
Unfortunately, the button was too short for the rounded edge of the hanger, so I had to improvise in the meanwhile. That is in fact paper super glue onto the button head to add some height.
It's not pretty, but it works. Which is a good tagline for the first iteration of the design.