Presence sensing using your phone has as much to do with your phone’s GPS as it does the ST app, as in, presence issues for phone devices can’t always be blamed on the ST app.
Presence detecting on my girlfriend’s iP6 and my Samsung Galaxy S6 has been damn near flawless. In the entire time I’ve had two false positives (which is bad for various reasons) and good handful of false negatives, i.e. sometimes even though we’ve come back, it might take 30 seconds or so to realise that.
The two false positives where when were were parked about a mile from our house and what you need to realise (about Android at least) is when it can’t get a GPS lock it can start doing things like substituting your GPS position with estimations based on mobile cell information (which sometimes just results in a ZIP code) or even based on what WiFi MAC addresses of hotspots are nearby.
There’s definitely improvements/extra safeguards that ST could make in this area though.