Google is out with an update to their once dead-simple notepad app, Keep. As the update rolls out, Keep users will be able to get reminders from their notes, based on a time or on a location. Which is quite neat for grocery lists, oil changes, and numbers and quotes you're going to want to remember later.
Timed reminders are no big thing, when it comes to a phone's resources. What is a computer, after all, but an adding machine running on a clock? But the location-based reminders, those are something involving your phone checking in with a satellite every so often, and triangulating from nearby Wi-Fi spots and cellphone towers. Signal strength requires power, and modern smartphones are not suffuse with excess battery power these days.
You know something about the convenience and longevity trade-off if you've used Locale, Tasker, or another if-this-then-that system for Android. iPhone users might have left a location-monitoring app like Google Maps, Foursquare, or Facebook's messenger running for a a long while and noticed the thing, too. The thing is that your phone is about to shut off at 3 p.m. It's a fact that, like yourself, the more your phone is awake and working, the more it eventually wants to go to sleep.
So what about Google Keep, which uses Android's new geo-fencing utility to monitor where you are, and whether you're walking, driving, or biking? Not a lot of specifics are available. A StackOverflow question on this topic remains mostly unanswered. From the look of the Google Play services specification, it's up to the developer to choose the priority: very concise location or "optimized for battery," which is described thus:
Uses low-power sensors to recognize the user's current physical activity
Developers are also advised to connect their app to location services when they're running, but immediately disconnect when they're in the background. But that's all that I can determine about geo-fencing from a non-coder perspective. Ditto with the Fused Location Provider and Activity Recognition APIs. Google can track you, and has "low-power sensors" it can call on to do that.
So, as with most "Android can do that now" moments, you're going to have to watch your phone, see how it does day to day, and decide on the battery trade-off. And I've decided I need to find someone who knows a lot about battery life in smartphones and do an interview with them. Know anybody?