So after shutting down sim808 and putting the stalker to sleep, results improved somewhat... But the improvement was just not good enough for what we expected. Measuring current draw from the battery yields a whooping 15mA - what in the world could be causing this?

The one thing we never suspected would dissipate much power when left unused - HC-SR04. The idle current we measure amounts to anywhere between 2.5 and 2.6mA, and since we got 5 of them, as well as a temperature sensor which leaks 0.6mA, things quickly get out of hand.

It is obvious that these sensors must also be turned on and off on demand. For this, we need an efficient, low power electronic switch. No such thing built in, of course, so we decided to hack one in ourselves.

The plan is simple - install a mosfet (2N7000) switch between the stalker 3.3v power output and the sensor shield power input pins, and control it using arduino pin 3 (literally the last free pin we got).

With this in place, we expect to drop down to 1mA ranges and finally be fully viable as a self-sufficient device with low maintenance cost.