I have a 240 volt smoke alarm with a green and red LED. The smoke alarms which are giving no trouble have their green LED "on" . I am guess that it is indicating 240 volt is ok. However I have another detector which has both the red and green showing and i have just replaced the battery. It begins to beep after a while. I think it is a Exelgard SMoke alarm but the labelling is not a good standard . certainly no model no.