#!/usr/
Members at Unallocatedspace are issued a barcode upon paying their first dues. These barcodes are used by the barcode scanner to check you in when you are at the space. The Checkin Service manages these barcodes and provides an interface for other services at the hackerspace to query the list of checked-in people.
This way you can just check IRC, email, or whatever to check to see if someone is at the space.