So, I figured out what was happening last time. It turns out when you start a monitor interface from the wlan0 it defaults to channel 1. So, you have to start it with
sudo airmon-ng start wlan0 4
Oh course, replacing the four with whatever channel your access point is on (most wifi points are on auto so it might be wise to set it on a specific channel).
Anyway, so I found the right command to use which is
sudo tcpdump -i mon1 -elnq "type mgt subtype auth and wlan host 00:11:22:33:44:55" |sed s/^/\\a/
Oh course once again replacing the mac address with the mac address of the device you want to filter on. The line will output a success at the end which is important to check for as if someone were to use a mac spoofer and try to authenticate then they could get in if we didn't check if the authentication wasn't successful.
I have some python code to run this in the background- it's in the github repo. I didn't include the settings file that includes the MAC address for my phone. Not a huge security problem, but you can never be too careful.
I ordered a new part. A little sensor- HC-SR501 Human Sensor Module Pyroelectric Infrared to detect if someone is at the door. It's got it's own control circuit and can be easily attached to an interrupt.