There are many things that can prevent Windows from entering sleep mode, not just mouse or keyboard input. I have problems with Plex not allowing my PC to enter sleep mode. The problem with ESET is that when it's performing a scan Windows doesn't see it as an active process so it will enter sleep mode during the scan.
If you don't want Windows to sleep just change the power settings to never allow sleep. It's very simple. You don't need an app. I've already come up with a solution so why do I need to use an app?
There are a number of command prompts to study sleep behavior. powercfg -requests is the most useful. It shows which processes are running that will prevent Windows from entering sleep mode. I'm currently streaming and running Filezilla. Both of these processes will prevent my PC from entering sleep mode. This is a screen shot of powercfg -requests: