What Activated the lights?

As I have mentioned before; the long upstairs hall in this house is dark. Its even dark when the sun is shinning outside. So you can imagine how dark it becomes at night. We generally keep the bedroom doors that front that hall closed so what little light that would filter in from those rooms to the hall doesn't. As a result I emplaced a strong motion light over the Master bedroom at the end of the hall. Anyone leaving the master bedroom will activate the hall light which reaches the farthest end of the hall. Anyone coming up the rear stairs, as soon as hey pass the top step will activate the hall light which lightens the hall all the way to the Master bedroom. When your eyes are adjusted to near total darkness this hall light is almost blinding. Last night my dog (Shadow) and I turned early. We had had a busy day and the pup hadn't even time for an afternoon nap; so she was ready to turn in. My wife was involved with something on the computer so she said she would be up later. Every night, Shadow and I play for a bit before turning in. We were both on the bed and I was trying to get her paws, a game she delights in. We were both facing the bedroom door when the hall light came on. We both reacted to the light. Even though the bedroom lights were on, the hall light was bright enough to be noticeable. I waited to hear my wife come down the hall but no one appeared. So we went back to play and it happened again. I got up and went to the bedroom door and looked down the hall, Shadow ran part way down the hall. There was nothing and no one in the hall but us. Going back into the bedroom we both got back up on the bed, but instead of playing we watched down the darkened hall. We must have waited 10 minutes or so and had about given up the lights coming back on. Shadow was probably asleep. But the lights come on a third time. I was up and in the hall within seconds with Shadow right behind me. There was absolutely no one or anything that could have triggered those lights. We went downstairs and into the computer room where my wife was still playing with the computer. I ask her if she had any idea what was going on? She assured me she hadn't and reminded me that she moves very slow with the her leg problems, which I realize very well. So the dog and I went back upstairs to the Master bedroom. I settled in with a book and Shadow curled up on the foot of the bed and went to sleep. I must have read nearly an hour and we had no more unexpected lights until I saw the light go on and heard my wife moving slowly down the hall. Nothing as small as a mouse will activate the light so it was activated three times by what? I knew where my wife was, I knew where my dog and I were. We didn't do it. This happened several weeks ago to my wife (An earlier entry). We didn't know then what activated the lights and we don't know now what activated them. This has only occurred twice in close to a year, so it isn't an on going thing. So I would say its unlikely to be faulty lights. So the question remains what is activating the hall lights?