Small python application that scrapes a DD-WRT ARP Table and alerts you via text when a client joins or leaves the wireless network. I use it to figure out when my kids' cell phones get in wireless range after school. This effectively lets me know when they get home.
Requires installation of the pygooglevoice API created by Joe McCall & Justin Quick. Get it at https://github.com/pettazz/pygooglevoice.
HttpReader.py is only written to work with DD-WRT at this time, since that's the router I have. If you want to make it work for yours, you'll have to provide your own search string and webpage to poll.
Call main.py in a cronjob in the interval to poll the system. On the first run, a configuration file "tracker.cfg" will be generated. Edit this file before running it again.
The whole premise of this relies on the ability to read the ARP table of the main router. DD-WRT makes this table available on Status_Lan.asp which makes this easy in my case. If your particular router doesn't have an easy way to fetch the ARP table via a webpage, you'll need to come up with another plan.