It is good to train your ears, rather than rely solely on digital tuners that could break down, run out of battery, etc. You could use a tuning fork, as it would never ever run out of battery. You could have a digital tuner as your main tuner as obviously it will be more accurate, but also have a tuning fork as backup, as well as to train your ears.
Personally, I have a digital tuner, as well as a tuning fork (a standard A-440 tuning fork, meaning the note it sounds is A). Killer combo. Only way to ruin a tuning fork is to break it and even then, that might be difficult.