[Evan] has paid that attention to the problem of Christmas tree hydration, and to address the shortcomings of earlier designs has come up with a low water warning using an ultrasonic rangefinder.

For the range finder, [Lord_of_Bone] looked to an ultrasonic rangefinder. For the ammo counter, [Lord_of_Bone] chose a proximity sensor. To run everything, the Raspberry Pi Zero was used and the ...