Auto-Switching your Bluetooth headset using SystemD

I've been struggling with this for quite some time, but today I wanted to fix this somehow.

I use Pipewire which has a pipewire-pulse package on Archlinux that interfaces with PulseAudio applications.

However, I had to manually switch the sink to make my Bluetooth device the default.

Usually, one can do

pactl list sinks short

Then

pactl set-default-sink <sink-name>

This will set it, which is what I do via the system tray option. But I wanted an automated solution.

At first, I tried to use udev but I couldn't figure it out, but SystemD made it easy.

So I created a file under /home/leon/.config/systemd/user/switch_bt.service with the following content

[Unit]
Description=Switch sink to the Bluetooth device
After=sys-subsystem-bluetooth-devices-hci0:256.device
After=sys-devices-pci0000:00-0000:00:14.0-usb1-1\x2d7-1\x2d7:1.0-bluetooth-hci0-hci0:256.device
BindsTo=sys-subsystem-bluetooth-devices-hci0:256.device
BindsTo=sys-devices-pci0000:00-0000:00:14.0-usb1-1\x2d7-1\x2d7:1.0-bluetooth-hci0-hci0:256.device

[Service]
ExecStartPre=/bin/sleep 10
Type=oneshot
ExecStart=/home/leon/.config/switch_bt.sh

[Install]
WantedBy=sys-subsystem-bluetooth-devices-hci0:256.device
WantedBy=sys-devices-pci0000:00-0000:00:14.0-usb1-1\x2d7-1\x2d7:1.0-bluetooth-hci0-hci0:256.device

To find the PCI device you can do systemctl --all -t device, you can search for the hciservice.

Then I simply enabled the systemctl --user service.

$ systemctl --user daemon-reload
$ systemctl --user enable switch_bt.service
$ systemctl --user switch_bt.service

The contents of switch_bt.sh is

#!/bin/sh

pactl list sinks short
pactl set-default-sink bluez_output.EB_06_EF_5E_E6_77.a2dp-sink

/usr/bin/notify-send 'Changing Default Sink' --expire-time=4000

So whenever I connect the Bluetooth device it waits for some time and then auto switches the sink to my Bluetooth device.