iPhone randomly moving out and in to geofence

[peterathans]

I recently started seeing an issue with our iPhones and how they send geofence information, and I was wondering if anyone else was experiencing the same issues.

 

I have a program to turn on the outside lights when either I or my wife enters a geofence around our home (200m dia) after sundown.  I then have another program to turn the lights off when we go to bed.

It's been running great for over a year, but in the last week or two I've woken up to find the lights on, and examining some state variables shows that there was a random geofence exit (and subsequent enter, from one to ten minutes later) sometime overnight.  It also appears that this random exit/enter occurred while the phone was being used (read emails, the news, etc) but obviously the phone never leaves our bedroom.  We're both running iPhone 7 v13.3

I can hack together some logic to ignore any more arrivals after we go to bed, but I'd really like to know what's causing this, and if it's something with my setup - again, I haven't changed any ISY or MoboLinc settings, this just started randomly happening.

I'm afraid the answer will be "MobiLinc just relies on IOS to provide location data, so the problem is with Apple", but any other info would be appreciated!

[simplextech]

This is a normal and natural phenom with GPS devices.  Higher end GPS units use a "pinning" method based upon some configuration.  Typically such as "Ignition Off" to then pin the unit to the most recent coords until it again gets a "Ignition On" to retrieve new info.  This prevents the spastic jumping that GPS units do.

Depending on GPS unit, chip etc this jumping varies and can be mild or throw the unit into another country all together at Warp speeds.  There's different software things done to try and work around this but the only method that is perfect is the "pinning" method. 

 

[peterathans]

Understood, but why then has this program worked flawlessly for so long, and just recently become unstable?  This issue is happening almost every night.

I'd be tempted to say that an IOS update changed the way the iPhone calculates its location, but I don't think my phone has updated for a month or so.  Or maybe the issue has been around for longer than I realize, and I just didn't notice it.

Since the phones are in our bedroom, is GPS the primary means of geofence location here?  Would an unstable wifi and/or cell signal cause it?

[simplextech]

What app are you using?  Some use A-GPS which are assisted meaning uses wifi and or cell tower locations for proximity.  Some GPS chips do a fall back to this as well.

Many things including electro magnetism changes of the Earth cause spikes and changes to GPS signaling and so does outside interference as it is just a low level radio signal.  There are way too many things that could be the cause of this.

Phones just aren't reliable GPS units for automation.  There's too many variables and changes that can occur.  They are better than some of the super cheap GPS units from ebay or even amazon but those are garbage in use as well.  Even some of the more major GPS devices in practical use for automation are garbage because of the jitter they have. 

Why this "just started" happening... dunno.  I suspect it has always happened but to a lesser degree that didn't cause notice.  Did you decrease the geofence size recently and then start noticing this?  There's just too many possible "why is this happening" to give a good answer.

[peterathans]

I'm using MobiLinc Pro, and haven't changed any settings in that app for a year or so...

[Geddy]

In the past I would have issues when hitting a dead spot in the house that I would drop wifi and hit a local cell tower and in the time it took to hit the tower my GPS location would jump. It was far enough outside my geofence that it would trigger some programs. I ended up making the geofence bigger to include the local tower for issues like this. It helped. I ended up getting a mesh network router to do away with dead spots and that worked even better. 

Perhaps this is happening with your phone all of a sudden too. What hurt more for me was that we live somewhat between two towers and the stronger tower was already inside my fence, but the tower went down for service so my phone jumped to the second tower that was outside my geofence. 

I'm on iOS13.3, MobiLinc Pro v4.17, and ISY 4.7.3 - haven't had problems since getting the TP-Link M9+ Mesh Router!

(My troubles were on iOS 12.x last winter/spring)

Since you say yours is happening overnight it could be your ISP rebooting their service/modem causing your phone to lose wifi and jumping to a tower.

 

[simplextech]

Issues like this is why I don't use phones for geofencing.

[InsteonNut]

@Geddy

You are dead on and a great write-up as to how this can and does happen. One more reason this could happen: If a neighbor moves in and brings their Wi-Fi router with them, the old location of that router follows that router for a while. It's also possible that if your phone drops off your local Wi-Fi but sees that neighbors router (it doesn't have to log in...just seeing the public SSID is enough) iOS may think your phone is near that router's old location. This does resolve itself, but takes time.

To protect against this, I usually recommend adding logic to your geo-fence programs to disable them during the period of time that makes sense to you. So, if after 10pm no one is leaving the house, disable the geo-fence programs till the morning.

Wes