I can usually tell by the sound that my bobbin is getting low, so start paying more attention That's easy enough when chain piecing. Last week, I was focused on joining 2 rows of blocks. At the end of the 90" seam, I found that I had only actually sewn about 2". Grrr...
Although I used to think a low bobbin warning would be nice, several people I know have them and when we sew together, I have realized that they actually start going off LONG before you are actually out of bobbin. So they end up either over-riding the warning, ignoring the warning, or turning it off!