BTphone

Bluetooth RSSI phone monitor script to activate screen saver.
Script for MACOS and Ubuntu 18.04 to run periodically from crontab.

MACOS (Tested on Catalina)

Requires /usr/local/opt/blueutil/bin/blueutil via homebrew:

brew install blueutil

Ubuntu (Tested on 18.04)

Requires hcitool and bluetoothctl:

apt install bluez

Install:

Requires that a active phone pairing exists from MACOS/Ubuntu to enable RSSI polling.
Locate and write down your phone BT MAC address when you set up the pairing.

Update the MAC="00:00:00:00:00:00" field in the script.
Set the number of loops per crontab call to scan for phone more than once a minute.
Default is LOOPS=1.
Alternativly set POLL=1 to continuously scan for phone presence, this will ignore LOOPS setting.
To use longer cron call intervals update the TIMESLOT=60 setting corresponding to your set crontab interval, converted to seconds.

Copy script to /usr/local/bin/ and make sure that it is executable
Run crontab -e and add:

* * * * *  /usr/local/bin/btphone.sh

Check your RSSI level manually via btphone.sh -v and update the RSSIlevel="" parameter in the script somewhat higher.
For MACOS the raw RSSI value is available but for Ubuntu the value is almost always 0 when close to the BT radio.

The file /tmp/btphone holds the last query result and the file /tmp/nophone exists if phone has been not been detected or RSSI value is over RSSIlevel.

The script sends notifications to the desktop whenever the phone is away or comes close again, just comment those lines out if it gets annoying.

That should be it...