Apart from crowdfunding, how can someone build a wearable tech product business which requires at least $500K just to start? Are there any government grants available here in the US?
Assuming you have people with relevant skills, you do not need $500k to start a wearable tech business. That kind of budget indicates to me you're already thinking about production, which is way past the starting stage of the business. Downsize your expectations to what you need for R&D, customer development, prototyping, and demand-generation.
Once you have demand, funding is much, much easier. Hardware products in particular have many more options for traditional financing through loans if they can show waiting orders. Kickstarter is actually used more as finishing funds and a pre-order platform for a lot of successful hardware projects than it is as starting-out funding. And it's always easier to get an investor when the money is going toward scaling instead of R&D.
To get the money you need to start the business from the ground-floor, some options to look into are:
For government grants, check http://www.grants.gov/ -- there are a lot of grants out there, but it's pretty hit or miss on if any are applicable to starting any given business.