National Data Buoy Center. It's one of the things our government did well and I was once a tiny cog in the corporate machine that sold these buoys to Australia and some other Pacific rim countries. Did you know they're putting actual cameras on the buoys so you can see what the ocean looks like in the middle of nowhere?
So like anything else, if you want one of these buoys to work all the time, you need to buy at least two and be willing to pay $50,000/day to send a working ship out there that can service the buoys for you. As you click on the various DART buoys at the website you can see where some of them have gone dark. It's like finding your sentries asleep at their posts with the enemy just over there, waiting.