How to fund a hardware business which requires a lot of capital just to start?

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:

• seed-stage investors - "seed" can still be pretty broadly defined, but there are investors willing to put money in at the idea stage if they can see the vision, the market, and a team that can connect the two.
• hardware accelerators / incubators - places like Bolt.io provide money, mentorship, and equipment access (getting rid of one of the big costs for starting a hardware business)
• business plan / entrepreneurship competitions - hardware startups actually have an advantage in live competitions because if you have any kind of prototype, the wow-factor for judges of being able to see and hold something real is significant.
• university research grants & fellowships - a lot of engineering universities are very interested in things like wearable tech. Places like the MIT Media Lab have an entrepreneurship program purposely built to help students go from idea to prototype to market.

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.