[usr1106]

Many potentially dangereous contacts happen inside where positioning doesn't work. Maybe in a restaurant the location could be inferred because you enter and leave through the same door. But in the subway/metro/underground? Also every high-raise building would create lots of false possitives by people that did not get close.

[jazzyjackson]

Google location is still very good in buildings and subways because they wardrive open wifi routers to help triangulate you. So when I'm near a wifi router with a particular MAC address that google has seen before, they've got me.

Agree with you on high rises and false positives, but then again, if air is circulated in the building or everyone uses the same elevators, might be worth notifying them.

https://support.google.com/maps/answer/1725632?hl=en

[uep]

Phone barometers can be used to get a pretty good idea which floor of a building you're on.

https://www.popsci.com/gadgets/article/2011-10/so-um-why-doe...

https://www.engadget.com/2012-09-06-stmicroelectronics-detai...