Location based alerts do not kill the battery, API explained.

Discussion in 'iPhone' started by jellomld, Jun 10, 2011.

  1. jellomld macrumors newbie

    Jul 19, 2009
    Apple introduced something called the "Significant location change API" with iOS 4.. And improved upon it in iOS 5. This allows your phone to monitor cell tower strength (as it already does) to determine if your location has changed dramatically, and then uses the "A" in AGPS (the assisted part) to grab the location of the new tower/wifi you're around.

    The location badge in the status bar will stay on even if a App only uses the significant location change API... so it's not always a sign your battery will be killed, I use latitude constantly to track my location and it never affects my battery life dramatically.

    The GPS is not activated unless the accuracy level the developer requests is really small. (most developers, including apple, won't use the gps radio at all)

    Apple uses a very large area for locations in the new reminders app, so battery life isn't hurt. I've been blocks away and still had the reminder set off.

    Again, battery life is not changed dramatically, I think some testing I saw a friend do with his app (that uses the api) decreased battery life by 2-3%. All the apps use the same API, so adding more location based apps doesn't change the amount of battery life used.

    Apple's explanation:

    "You can request events for significant location changes only. This provides a more limited set of tracking options but offers tremendous power savings and the ability to receive location updates even if your application is not running. This service is available only in iOS 4.0 and later and requires a device with a cellular radio."

  2. jellomld thread starter macrumors newbie

    Jul 19, 2009

    Can't wait to see all of the anecdotal "evidence" some people post that this isn't true.
  3. kdarling macrumors P6


    Jun 9, 2007
    First university coding class = 47 years ago
    Cool info. However, two corrections:

    1) It doesn't monitor cell tower strength (which could change just by putting the phone in your hand), but instead watches for changes in the cell towers it sees.

    2) The "A" in AGPS refers to getting satellite information, not cell tower or WiFi locations. AGPS only refers to GPS methods. WiFi and Cell Id are separate methods, and are related to that cache file that had so much publicity last month.
  4. apprunner macrumors regular

    Jun 26, 2010
    on #2. A in AGPS uses the cell-towers to assist the satellite GPS function. The OP is right.

  5. Rodimus Prime macrumors G4

    Rodimus Prime

    Oct 9, 2006
    I am glad someone explain that.

    Rough location as I like to put it is what most Apps use (android, Blackberry, iOS ect) and rough location requires zero battery power to do because it is going to be based on the location of either cell tower or wifi both which are generally stored in a large data base elsewhere. That gives them the rough location and for most location based stuff that is good enough. Weather being a big one because that is based on where one of the local weather stations is and lets face it those are spaced out quite a bit. Adds or things like four square only need the rough location to give you a choice from shops and you can search to speed it up.

    read your link.
    OP is wrong. aGPS means that it uses cell towers to get the current location of the sats and to speed up the lock on processes but still requires your GPS attenuate to power up. One other trick it helps it do is the cell tower is a known fix point so it can be used to help correct errors in signals in the sats as it is monitoring them to so it gives the phone a bit more info on what it needs to do to fine tune its location. Other wise it uses one of the sats to do it but that can only get you with in about 3-4 ft or so. Father you are from the fix known bases station the more errors that can crop up.
  6. jellomld thread starter macrumors newbie

    Jul 19, 2009

    AGPS as found in the iphone does use wifi and cell tower calculations to speed the actual GPS lock.

    However, apple is clever, they have their own location database (or they still ay use skyhook wireless) to determine a rough location of the user without using the GPS chip. This is how the ipod touch is able to grab a rough location without having a GPS chip, or a cell modem.

    When using the significant location change api, the location isn't gathered by the GPS chipset at all, it's gathered from the change in cell tower information/wifi. If a location cannot be determined, gps will fire up (from my understanding)
  7. apprunner macrumors regular

    Jun 26, 2010
    You are right. I thought the agps chip may read the cell tower information and can triangulate the relative position without turning on the satellite portion however, it seems that this function could be enabled on the OS layer instead.
  8. Rodimus Prime macrumors G4

    Rodimus Prime

    Oct 9, 2006
    The triangulation part I think people get confused on is part of the e911 system and more done carrier side to get your position for 911. It a little processor intensive a cell to do and it can be done quicker server side and a system that is designed to work no matter what the phone is. Now that can only get you down to about 300 ft radius but for 911 and is generally close enough.
  9. Krevnik macrumors 68040


    Sep 8, 2003
    This is really the problem, IMO. There's no difference between someone who's subscribed and my turn-by-turn being left on (which I'd want to address). It makes the status icon less useful as an indicator if it is always on because of a reminder you set.
  10. torresus macrumors newbie


    Oct 13, 2011
    Based on what I've read in this post (and it's been very helpful) I recommend the following:

    Go to: Settings>Location Services

    Scroll down to the bottom and select "System Services". There, you can see that "reminders" are not constantly using a GPS signal...much less AGPS (read the icon explanation). Now, rather than killing Location Services on everything which would pretty much defeat the purpose of having a "SMART" phone, you can choose what signals not to use by sliding them "Off" (if you're that anal about it). Or, if you don't even want to know about Location Services running or not and just adapt to your battery life as is, scroll all the way down on this page and switch the "Status Bar Icon" to "Off". If you've ever used Android or Windows Mobile, your iPhone battery life still exceeds those characters! Ha-ha!

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