Welcome to the club! This has been a problem since the introduction of the Nexus 10, and Google refuses to address it. Mine is about 3 weeks old, and I've constantly fought it, with no results. It seems to have gotten worse since DST started in the US last weekend. I would have it replaced under warranty, but what my internet research has found is that this doesn't solve the problem. I'm convinced it is a software problem, and not a hardware problem, since things I do to try to fix it will produce different results. Sometimes it will work for many hours before screwing up, and sometimes just mere minutes. I love my N10, but am very disappointed in Google for releasing such trash. I would like to use the alarm function, but it is just not reliable. Very sad!