I picked up the pieces to do this in my M235i a couple days ago. I ended up going with this equipment:
ScanTool 427201 OBDLink LX Bluetooth - $50
https://www.amazon.com/ScanTool-4272.../dp/B00H9S71LW
I have an iPhone, so using my phone with it was a no-go. Also, my iPhone is a 5S with a 4 inch screen so I wanted something larger. I picked up this phone from Amazon:
BLU R1 HD - $60
https://www.amazon.com/BLU-R1-HD-Exc...dp/B01H2E0J5M/
I got the version with the Amazon special offers, so it shows ads on the lock screen. This isn't my primary device so I don't care about that. This is a surprisingly nice device for $60. I don't have a SIM installed in it because I don't need have a need for that. The phone is installed in this holder:
Belkin Car Cup Holder Mount for Smartphones - $30
https://www.amazon.com/Belkin-Car-Ho.../dp/B00NL7GTXG
For the app I'm using Torque Pro from Google Play:
Torque Pro - $5
https://play.google.com/store/apps/d...l.torque&hl=en
I've automated things a bit using Macrodroid:
Macrodroid - Free - $3 for no ads
https://play.google.com/store/apps/d...crodroid&hl=en
My automation works like this:
1. I wake up and unlock the phone. Macrodroid turns on bluetooth, waits 1 second, launches Torque.
2. If I lock the screen Macrodroid asks Torque the quit and turns off bluetooth.
3. If I happen to forget to lock the screen manually when I'm done, when the car turns off the lighter, which my phone detects as power being disconnected, Macrodroid asks Torque to quit, turns off bluetooth, and locks the screen.
4. If the Light Sensor increases to 25lx, wait three seconds, if still 25lx, turn the screen brightness all the way up. This makes it easier to see in sun light. Auto brightness on the phone itself doesn't bring it all the way to 100%.
5. If the Light Sensor decreases to 10lx, wait three seconds, if still 10lx, turn the screen brightness to 10%. This makes it less bright at night.
This way Torque is only running when I unlock the phone. If I don't want to see it, I lock the screen and Torque disconnects from the car and bluetooth turns off. I don't have to worry about it being connected when I don't want it. So far everything works pretty well but I'm only a few days in.