Answering questions on this forum has been the number one way I’ve learned. My personal HA system is pretty modest compared to most but through answering questions my knowledge has expanded way beyond my personal needs. Especially when it comes to coding rules. Don’t hold back.
NOTE: The Docker deployed OH does have some limitations. See this posting for my experiences with it. Overall I’m really happy but if I needed to use the Exec binding or Network binding I would be disappointed.
If you are not afraid of a little DIY, you probably can’t get any cheaper than a PIR and an ESP8266 and some MQTT comms. However, unless you have a 3D printer or are good at fabrication the aesthetics of the commercial units, overkill or not, will be much better than most DIY projects.
I posted an Ansible playbook that does that (and a bit more) here:
Your approach works as long as you make light use of persistence. If you are using rrd4j or MapDB to store the state of every Item every minute that will be a lot of writes as well. However, you most likely do not want to wipe these out every day at 3 am.
Or the Network Health binding to detect when your phone is home through pings. Scripts running on routers are also commonly used. I have a Python script that does this for BT as well.
Or use the My.openhab binding which supports OAuth2 connectivity to IFTTT (there is an openHAB channel). No open ports or dyndns mess to deal with along with all the security risks that comes with that.
The security engineer in me see this as an argument against my using this technology. Also, due to interference, it is important to limit the number of wireless technologies you are using. I’ve got WiFi, Zwave, and RFM69HW and I can already see some evidence of interference between the three.
There is a long thread on how to get that to work using hping.
However, I rely on a combo of just standard Network Health and BT detection and it works like a champ.
There is also a Caldav binding that will let you connect to your calendar directly rather than going through IFTTT, if you so choose. However, I don’t think there is a working version of this binding for OH 2 yet.