Also -- while Fi nagging you about your low hearts is really lame and stupid (with no way to avoid the message other than healing, meaning that if you want to know the name of an enemy when you only have three hearts, Link calls Fi out, she tells him his hearts are low, she goes back into the sword, and then he calls her out a second time, which is almost as dumb as the times when she tells you something in a cutscene, goes back into the sword, the cutscene fades out, it fades in to gameplay, and Fi comes out again and tells you what she just told you, only more explicitly), the one-heart beep is very unobtrusive. Almost... too much so. It should stay the way it is when just walking around, but I think it would add a lot to the tension if the sound got more urgent when you have one heart left during a boss fight, and maybe even more so when you have a fraction of a heart.
But hey, if I'm telling a Zelda game that its one-heart beep isn't annoying enough, that in and of itself is a monumental leap forward for the series.