Pokémon GO: 7 Essential Battery-Saving Tips You Need To Know
5. Use And Understand The Battery Saver Option

Thanks to the spectacular lack of tutorialisation in PoGo, the 'Battery Saver Option' in the settings can easily pass you by - especially seeing as triggering it, doesn't appear to do anything.
Instead, it only relates to when turning your phone upside down, the screen will turn off whilst the app stays running. This is useful for pocketing your phone and walking great distances with the app still active, as nothing actually happens or tracks if your phone is asleep.
For clarity's sake: Pokémon don't get closer to you, eggs don't hatch - nothing.
By using this method, attach headphones to your device and simply listen out; the game will make a noise when you're close to a PokéStop or if a monster has appeared in your vicinity, then you can grab your device and ready your Pokéballs!