Good idea. I have implemented this setup for my upstairs hallway light, so if anyone gets up at night, lights come on dim. Works great, but the only problem i foresee is if you need to have a light(s) on during the day for some reason, it would keep going off every time motion is detected. Probably not going to be an issue for your garage, or my hallway, but other locations may have issues.
I wish there was a way to combine the quickness of a hard coded scene and the flexibility of a program . I think my remaining motion sensors, i am going to control them with programs. Hate that 1-2 second delay, but hard to get things working correctly without using programs.
By the way, can the 2420M's be used outside?