Started to look into the battery life this evening. Planned to have two hall effect sensors one for shower door and the other for shower curtain orientations or maybe 4, 2 for each orientation. The best case A3144 supply current draw is 4mA per the datasheet, less than 2 days of stand-by for just the sensors with 150 mAh LR44 coin cells.
Found a similar Allegro A3214 with a 6 μA (typical) supply current (datasheet 22 μA max is still better than 4mA). Will need to order some of these. The supply voltage range is also reduced from the A3144 that happened to work under the minimum data sheet supply voltage. Plus these ones are not magentic pole sensitive.
The MCU will be in low power mode most of the time so 1 μA or so.
A buck-boost converter will maximize usable battery life. The energizer cut off voltage was .9, so 2.7V for 3 cells. Might look to see if I can find a drop in board that will work and fit in the case.
Another option is to power the hall effect sensors direct from the battery. When magnet is detected they would enable power to the MCU and rest of circuit. The buck - boost converter could remain in shutdown mode saving more power. Prototype with a linear regulator should even get decent battery life.