Presence detection platform using bluetooth devices, re-use an old Smarphone as a presence detection manager, when detecting a allowed device, it will communicate it through MQTT then with HomeAssistant you can do the presence automation.

Prerequisites

MQTT Broker
Home Assistant
Old Smarphone Android

Setup
1 Open App
2 Menu Wizard configuration
3 Room settings (Don't forget to click save to save the changes)
4 Add Allowed Devices, add the devices of each member of your family or friends
5 Configure MQTT client, set up the MQTT client, check the connection to your MQTT broker ((Don't forget to click save to save the changes)
6 Click Done
7 Now you can press play and a background service will run, every minute
or the time you configure in options, it will make a discovery of the devices around it, if it matches one with the list of allowed devices it will send it with MQTT

Integration with Home Assistant
For integration into Home Assistant is done using an mqtt sensor, see example

configuration.yaml

sensor:
- platform: mqtt
state_topic: 'andrews_home/first_floor/FF:00:11:22:36:11'
value_template: '{{ value_json.confidence }}'
unit_of_measurement: '%'
name: 'Andrew First Floor'

The mac address of the bluetooth device is sent as part of the topic mqtt

How the confidence value is obtained?
Confidence value ranges from 0 to 1.0
If a device is found it increases by 0.5
If a allowed device is not visible the range of bluetooth detection, it is decreased by 0.33