C-a _silence [on|off|sec]
Toggles silence monitoring of windows. When silence is turned on and
an affected window is switched into the background, you will receive the
silence notification message in the status line after a specified period
of inactivity (silence). The default timeout can be changed with the
silencewait command or by specifying a number of seconds
instead of on or off. Silence is initially off for all windows.
None yet.