nixos

I decided to switch to NixOS on my desktop and so far it's been great, I love being able to build out my config in the Nix file, but there is one thing I've not been able to figure out how to change. After a period of inactivity, the computer suspends (or hibernates?) and basically turns off (all the fans and lights turn off and it disconnects from the network, I don't know if it's saving the state in RAM of the drive). How do I get it to not do that and just lock the desktop and turn off the screen after inactivity? I'm using KDE Plasma and I've tried different kinds of configurations that build successfully but still don't prevent it from going offline.