In the past few years, we have covered plenty of app connected coffee makers here. If you are serious about your coffee, you may want to invest in a TDS refractometer. The DiFluid R2 Extract is an app enhanced coffee refractometer with 3 modes (auto, multi, standard test). You can use this device to figure out how strong your coffee really is.
This refractometer comes with ±0.02% precision and TDS range of 0-30%. It has a color display that shows the relevant data. It also has an aluminum sample dish and water resistant design. It has a 430mAh battery and lasts up to 2 hours.[where to get it] [official site]