There is nothing covering the sensor when you wear it. The band does not open into two pieces, the clasp just makes the band wider to get over your wrist, so when you lay it down the band lays across the back. If you look at the pick that shows the 3 colors here: http://www.amazon.com/dp/B00ZIMK1TA/ you can see the gold one is open and the others are closed.The band is quite nice, but what is under it, preventing the sensors from touching skin?
By the way, it appears they have updated the pics on that link, and they no longer look exactly like what I got (see my earlier post for pics of what I got). Mine matched the pics at the time I ordered it. Now the pics look more like the ones that others are getting like this: http://www.amazon.com/dp/B00ZOR2GTC/ or this: http://www.amazon.com/dp/B00YOLUBEG/ so now it seems the only advantage to the link I provided is the price. Save money, but wait longer for it to ship from China (assuming updated pics are accurate).