SIMPLE SOLUTION!:.....I had this same problem and have a whole discussion about it here somewhere. Bottom line turned out to be that my DVR (DirecTV also), when activated by my logging into sling remotely, energized the HDMI output from the DVR to my TV. Well, many of the newer TVs (mine is a Samsung 60" smart TV) will automatically turn on when they see an active HDMI connection. When at home, I thought I was turning on my tv with my DirecTV remote....while actually it might have been coming on by itself just seeing the active HDMI connection from the DVR. Then I remembered my BluRay player does the same thing! This feature can be turned off in most TVs. It was funny, I would watch something using Sling, but get an alarm from my security cameras at home....I'd log into my security cameras and see the TV was on in my family room! What? Who's there?!? Although it gave my home a "lived in" look while I was gone, I too, like you, did not like having the TV on when I wasn't there. Although, as mentioned above, this feature is likely selectable in the TV menu/settings, I kind of like the feature, so my solution was to simply unplug the TV when I leave home.....it's probably a good idea to leave it unplugged anyway as it protects against electrical surges etc......and, it definitely solved the problem!
For many years I have been watching TV on my computer with a sling box connected to a DVR, first Comcast now directv. I only use one wire to remotely turn on my dvr. This has been working fine. Recently without making any changes to my setup the remote from my computer while I am logged on will turn on the tv while I am using my computer to watch live tv or recorded shows on my computer. I do not need or want the tv turned on since I am not there to watch the tv screen, I am watching on my computer. Any ideas why this suddenly changed?