[Jon Stratis]

Interesting idea, Blake. Sure, phones/tablets/laptops would automatically connect to a known SSID when in range, but they can only connect to one network at a time, and presumably other networks in range (like a school wide wifi network) may take precedence for the device (either due to precedence settings within the device, or because they were already connected to that network when they came within range) and thus provide inaccurate results. Your wifi router would also need to be connected to the internet, otherwise people would have to be constantly manually connecting/disconnecting when they needed to get online. The good news is that you can easily find an existing router that will maintain connection logs, and you could easily write a small service to log into the router and parse them. Set it up on a cron job and you're all set.

It might be better to use bluetooth instead of wifi - you can have multiple bluetooth devices connected to a phone at the same time, and it won't risk killing the phone's default internet connection. Position it near the entry door so everyone would automatically connect (after they set it up as a recognized device) as they walked into/out of the build space. Your software would then just have to be intelligent enough to detect first/last connections, recognizing that someone may connect a dozen times or more during a meeting as they move around the build space and come within range of the device.