til/mac/detect-how-long-a-user-has-been-idle.md

Detect How Long A User Has Been Idle

The ioreg utility on MacOS dumps the I/O Kit registry tree. This lets us look at the state of all hardware devices and drivers registered with I/O Kit. Looking specifically at the Human Interface Device subsystem (IOHIDSystem), we can find a handful of properties including the HIDIdleTime.

$ ioreg -c IOHIDSystem | awk '/HIDIdleTime/'
    | | |   "HIDIdleTime" = 91831000

That value is the number of nanoseconds since a human input device was last interacted with. That is the amount of time the user (me) has been idle.

I can convert this to seconds, which is the small amount of time between me hitting enter in the terminal and the command finding the idle time.

$ ioreg -c IOHIDSystem | awk '/HIDIdleTime/ {printf "%.2f seconds\n", $NF/1000000000}'
0.13 seconds

I can run this in watch to see the elapsed idle time increment.

watch -n 1 "echo -n 'Idle time: '; ioreg -c IOHIDSystem | awk '/HIDIdleTime/ {printf \"%.1f seconds\\n\", \$NF/1000000000}'"

After watching the idle time increment for a bit, I can move the mouse and watch it reset on the next watch loop.

This could be used as part of a script that takes certain actions after the user has been idle for a while, like putting the display to sleep or stopping a time tracker app.

There is a lot going on in the ioreg output and it's hard to make sense of hardly any of it. I found running ioreg -c IOHIDSystem | less, searching for IdleTime, and browsing from there to be a good starting point.