systemd – Running awesome-client (which uses dbus) from acpid

I set up a acpid rule to execute the following command, whenever I receive a specific acpi message:

awesome-client "activate_tabletmode()"

Where activate_tabletmode() is just some function that I want to call in my awesome config. I know that awesome-client uses dbus to make IPC with awesome possible.

I get the following error message:

Failed to open connection to "session" message bus: Using X11 for dbus-daemon
autolaunch was disabled at compile time, set your DBUS_SESSION_BUS_ADDRESS instead

Can someone help me understand what that means? I tried to run the command as user instead of root using sudo -u, but it did not help.