WiFinder
By using nmap, this script scan the number of hosts connected to the network, to play an 'alarm' when the value changes.
The aim is to be warned ahead of time (depending on the signal strength), before unexpected arrival of any roommates.
Install
To run the script are required Python and Nmap, which can be found at the following :
Also, take a look here : https://pypi.python.org/pypi/python-nmap