/lib/udev/bluetooth_serial is in bluez-pcmcia-support 4.101-0ubuntu13.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 | #!/bin/sh
#
# bluetooth_serial
#
# Bluetooth serial PCMCIA card initialization
#
start_serial()
{
	if [ ! -x /bin/setserial -o ! -x /usr/sbin/hciattach ]; then
		logger "$0: setserial or hciattach not executable, cannot start $DEVNAME"
		return 1
	fi
	if [ "$BAUDBASE" != "" ]; then
		/bin/setserial $DEVNAME baud_base $BAUDBASE
	fi
	/usr/sbin/hciattach $DEVNAME $HCIOPTS 2>&1 | logger -t hciattach
}
stop_serial()
{
	[ -x /bin/fuser ] || return 1 
	/bin/fuser -k -HUP $DEVNAME > /dev/null
}
case "$ACTION" in
   add)
	start_serial
	;;
   remove)
	stop_serial
	;;
   *)
	logger "Unknown action received $0: $ACTION"
	;;
esac
 |