First install libnotify, #pacman -S libnotify
Then notification-daemon and create The folders $XDG_DATA_HOME ; in there the folder dbus-1 and in there a folder services; in there the file org.freedesktop.Notifications.service
Edit with leafpad:
[D-BUS Service] Name=org.freedesktop.Notifications Exec=/usr/lib/notification-daemon-1.0/notification-daemon
Now start the service:
/usr/lib/notification-daemon-1.0/notification-daemon start &
Test with: notify-send "test"
Now add to /home/username/.config/openbox/autostart
a line with: start /usr/lib/notification-daemon-1.0/notification-daemon &
Be sure to have the Desktop Notifications plugin activated,In Services. Plugins.