Is there a possibility of outside signals activating system--ie: garage door openers or other homes with a similar x10 setup?
I've never heard of any issues with garage door openers interfering with the DS7000. Different frequencies & different codes, so highly unlikely.
The only way another home (neighbor) could interfer with your system is if you accidentally installed one of their security devices into your DS7000.
As
Dave_x10_L and
tom j suggested, the most likely culprit is the MS10A motion detector. I gave up on mine long ago because of their unreliability. Have you ever had a false alarm in
Home Mode? If not, then that should pinpoint the motion sensors as the source of your problem.