time-out plugin for the Xfce panel

xfce4-time-out-plugin is a plugin for the Xfce panel.  It's a comfortable 
tool for taking a break from work every now and then. You can define a 
working interval and whenever time of this interval has passed your screen 
is locked for a configurable amount of time - which gives you enough time 
to grab a cup of coffee, smoke a cigarette, or even do something healthy 
like eating, exercising, cleaning up or whatever.