If your idea involves a physical product , how did you get it built?

If your idea involves a hardware product, how do you go about building it?

For example, let's take a random idea "Smart Water Bottle", capable of measuring the amount of water I drink using sensors, etc, and send it to the phone to provide analytics in the app. For this idea to fully work, a water bottle should be designed and built as per requirements.

Did you ever build a product that included hardware? and how did you get your product built as per your requirements?

As a software developer, I have no idea where to start or where to look if the idea involves a physical hardware product and how to get MVP out as cheap as possible. Any guidance on this is appreciated. Thanks