I know there is another option by another contributor for using Fing with Indigo. However, I wanted to create an option that did not rely on AppleScript, and I wanted a bit more control over the variables that are created/updated. The program I wrote runs using node.js. It can happily be deployed on Mac OS X, as well as any other OS that node.js supports. I've got it running on a $40 Raspberry Pi device which is a awesome option if you are heavily reliant on the accuracy of detecting if you are home via network device presence.
As great as this is with Indigo, it will evolve to include other functionality to react to devices on a network. For example, the program has the placeholders to notify you when a unrecognized device appears on your network (using a white list). A little added security to your home automation network. It can also support sending a notification to any HTTP endpoint when a configured device appears on your network.
Until this is tested a bit more, I cannot guarantee it will work for everyone's configuration. If you are technical and brave enough to try it out, that's why I posted it! Good luck.
Code can be found here: https://github.com/mlamoure/Fing-Device-Watch