[tdj]

I developed a similar app for a psychology research team. They needed a way to trigger certain things (sound recording, etc) when two certain people were in physical proximity. As it turns out, bluetooth bonjour discovery did the trick when they were in the same room. Over wifi, it got triggered sooner, once one of them enterred the building where the other one was (which corresponded to being on the same LAN).

The hard problem on iOS devices (iPod touch) was keeping them awake during this, so they could detect eac other. iOS likes to sleep while locked. Got a solution, which made the battery last around a day. I guess they're not using mobile to mobile peer triggers, but fixed-to-mobile and then deliver a notification. Interesting to see this popping up in commercial tech.

I was going to spin my code out into a infrastructure for spatial awareness triggers for various home automation tasks, but also couldn't find a killer use case. I'll be following this topic for ideas :)