Wearable health devices represent an exciting opportunity for medtech. Pegged at $2 billion in 2013, the market for wearable healthcare products is expected to grow 65% each year, exceeding $40 billion in 2020, according to market research firm Soreon Research. And while one in 10 Americans owned an activity tracker last year, according to Endeavor Partners, a number of wearable health devices offer more sophisticated capabilities than simply counting steps. 

Here are some wearable health devices we're keeping our eyes on.