Hello,
I would like to present you a project now funding on Crowdsupply:
PowMeter Nano shield is a very tiny shield to mount under an Arduino Nano and that will let you monitor the consumption over the USB and/or VIN.
A 0.96 OLED display shows voltage and current and the user can program visual and hardware alerts. It can monitor up to 8 amps on VIN.
It is based on INA226 chip that gives a resolution of 25 uA on the USB power source.
The crowdfunding page is PowMeter Shield Nano | Crowd Supply
And there is a short tutorial on how to monitor voltage, current and raise alerts within your own program on the host Nano board there: PowMeter Shield Nano - How to Query Values and Raise Alerts With PowMeter | Crowd Supply