For years with a Mac Pro I used a "smart" power strip (the kind that has a "control" outlet that one plugs a computer into, which when it senses that the computer is asleep or off shuts of power to the other outlets into which one plugs peripherals such as one or more monitors, powered USB hubs, etc). I recently purchased a late 2015 iMac, and I'm finding that there seems to be some kind of "feedback loop" that prevents the iMac from staying asleep when used with the smart power strip. For example, I plugged a second monitor (connected via a Mini DisplayPort cable into a Thunderbolt port) into one of the "slave" outlets on the smart power strip. When I put the iMac to sleep, the iMac goes to sleep, and the smart strip dutifully shuts off power to the second monitor. Then, about two seconds later, the iMac wakes up on its own. If the second monitor is NOT plugged into a "smart strip," then the iMac sleeps (and stays asleep, as it should). The same thing happens with a powered USB hub, or any external drive, connected either via Thunderbolt or USB. The only peripherals that seem NOT to induce the iMac to spontaneously wake up after about 2 seconds are my external speakers (plugged into the headphone jack) and a wireless mic receiver plugged into a USB port (directly into the iMac). What's going on here? Is there a fix/workaround? It would be nice not to have all that "phantom" power being used, if possible.