Occupant presence detection is a very desirable thing for home automation. Among other things, it allows you to:
- Automatically arm and disarm your alarm system.
- Turn on porch lights or provide another welcoming action when you return home.
- Automatically sequence lights to simulate a lived in look when you are away.
I was going to create a post on how you can do this but found that it has been better covered by others. So if you are interested, consider reading the blog posts by Phil Hawthorne. In particular his post on presence detection is quite good.
If you are more of a visual learner, a different way to do presence detection is covered on the YouTube Hook Up channel. You may wish to look at the episode on Node-RED where presence detection is covered at about 3:30.