I've got an older (not antique) Singer that doesn't have any bells or whistles, but I've spent so much time sewing on it that I can tell by the sound and the "feel" when the bobbin is running low. Sometimes I don't pay close enough attention though, or try to sew "just a little bit more". Oops! :mrgreen:
My inherited-from-my-Granny Pfaff 7570 and her slightly older Pfaff (can't remember the model # offhand) are still sitting off to the side, waiting for me to learn more about them as soon as I have time. She passed away a couple of months ago, and we're still going through her estate. But I remember her saying how much she liked the low bobbin indicator. :)