I would put my notebook running Ubuntu to sleep by closing the lid or by choosing Suspend at night. I could see the display go off, harddisk turn off and keyboard lights go off. However, in the morning I would find this notebook fully active! How was it coming out of suspend mode in the middle of the night?
The culprit turned out to be a Targus wireless mouse that I had started to use recently. Any slight vibration of the table would awaken this mouse. It would communicate with Ubuntu informing that the user has moved it. So, Ubuntu would come out of suspend mode.
Now I switch off this mouse after I suspend the notebook. The problem has not repeated after I started doing this 🙂
Tried with: Targus AMW071 wireless mouse and Ubuntu 14.04