paul
I too wondered about the same thing. I plan on doing this with a motion sensor using the dusk/dawn feature which sends a unit code +1. I am using a MS16A sensor in my system. I use this motion sensor to trigger macros that set flags to tell if I'm Home or Away. A dummy module using a timer is set to trigger my lighting macro 20 min before dusk. Depending upon if I'm home or away the appropriate macro will run. Currently I'm not using the dusk/dawn feature, but in my mind using a smart macro, flags, and the dummy module using a timer I think I can get it to work and run the lighting macro if the lights need to come on earlier if it's an overcast day.
Right now I'm stuck in a mental ground loop. ??? I'm over thinking this project. :-
TTA and Puck have planted the idea of using the dawn/dusk feature on a motion sensor. Search the forum and you will find various ideas on motion sensor dusk/dawn feature.
In the mean time TTA posted a wonderful motion sensor comparion chart that is very helpful.
I always use this chart because it's more complete (and possibly accurate):
Comparison of X10 Motion Sensors (http://www.activehomepro.com/sensors_compare.htm)
In the mean time I will be working on trying to figure this one out. Christmas will slow me down a little. But I will post my results as soon as I can.
Cheers ;D