How can I see how long my computer has been active (as in not idle)

I've seen a variety of solutions to check how long my machine has been idle, and I know I can check how long since last reboot with uptime, but I'm curious if there's a way to see how long since my computer was last idle. Maybe since the last time the power save settings kicked in, or last time since the screensaver turned on / monitor turned off, etc? I'm fine using an applescript or shell command to determine this, if those are the best solutions.