But: Attention! If you flash the logger or disconnect the alarm device (control) from the logger the LED will be ON continuously! If you do not use an optocoupler in front then the 10k resistor here
http://62.153.249.80/jlog/wp-content/uploads/2011/06/Alarm_device_JLog2_v3.2up-2.jpg will avoid that. The only disadvantage is that there is no alarm in case of the alarm device is disconnected from the logger or the logger lost its supply voltage. But that kind of alarm w'd be anyway a continuously burning LED, "burning" in the meaning of the word, perhaps. (In case there is no current delimiting series resistor.)