First: entrepreneurs are too often convinced in the unparalleled genius of their ideas. Nobody is going to steal it. That would require dropping everything they're doing and committing to a long-term project with very little to go on. I suppose if you ever do get your idea "stolen" it's because it's too easy to execute (in which case you've come up with a commodity--go back and rethink it) or it's way too far outside what's realistic unless you're a huge company with loads of resources. The only exception I could see is intellectual property--some ideas are worth patenting if you think that you can get licensing fees down the line.
Second: Ideas aren't worth much. Customer feedback will make you change your idea and probably pivot your business model dozens of times, so share often and as much as possible. Plus, you'll get little to no feedback very, very slowly making people sign NDAs. By doing this, you're only hurting yourself.
Third: Carolyn Branco's answer is spot on, so re-read that a couple times. As she points out, start with discovering a need or problem from actual customers (not your friends). When you know the problem, then and only then should you prototype, which is the ultimate feedback tool. There are different kinds of prototypes (sketches, mockups, or working products) that you can use to assess the desirability of your product to customers. For tech products like yours, don't overdo it with UX/UI because you need a prototype that's easier to change as you get feedback. After you establish desirability with a certain market segment, get to work on the business model.
In summary: stay lean, get feedback from customers, prototype fast, don't skip ahead in the process and don't worry about someone stealing your idea.