How can I make assets update based on outside data?

I am looking for information on how to build an app that can take outside data as input but I haven't found anything. I'm not sure if I'm just not using the right language when searing or what.

I want to make an app that puts a voltage gauge on the environment and communicates to a sensor in order to display the voltage given by the sensor in real time. I have absolutely no idea how to do this and I haven't found anything online. I'm not even sure if it's possible.

Can anyone point to somewhere I could find information on this?

Thank you!