Ask HN: How to get started with developing Smart/IoT hardware products?

I have an idea for an IoT product that may or may not work for niche audience. My background is software, I have developed Dotnet(api), iOS and Android apps and lead engineering teams. Although I have learnt basics of microprocessor, computer hardware etc during my school, I have more or less no knowledge of it now.

Where do I get started if I want to learn and make smart IoT products. I want to make a ring with a touch screen and a button. For starters, It will act as a counter using button and remind users(notifications) on particular time of the day. I also want to develop a mobile app as a companion that will help configure the ring, set reminders etc.

Where do one start to make something like this? Are there any open hardware that can be used for the prototype?