Finding out which process inhibits monitor sleep, even after setting DPMS flags

My screens aren't turning off, using xset to set dpms off, suspend or standby they always turn on again. I know a way to figure out what event caused the system to wake up from suspend, but I haven't found something like that for dpms events. After a restart they behave again, which led me to blame some specific process that I don't usually do. I started manually quitting processes until I found steam to be the most likely culprit (there's a bug report about this issue ), but I could do without going one by one. Is there a event/log about which process/event causes monitors to break dpms state?