Many current measuring devices are only good for low side measuring and monitoring. This means that unless you want to get a battery involved, you have to place the measurement resistor between the target ground and true ground. Doing this can cause problems with circuits since electronics are prone to glitches when the ground references change and move with varying current draw. This breakout board from Adafruit is much smarter - it can handle high side current measuring, up to +26 VDC, even though it is powered by 3.3 or 5 V. It will also report back the high side voltage, which is good fro tracking battery life or solar panel output.
For more information visit the INA219 DC Current Sensor product page