slackbuilds/system/xautolock

Xautolock monitors console activity under the X window system, and
fires up a program of your choice if nothing happens during a
user configurable period of time. You can use this to automatically
start up a screen locker in case you tend to forget to do so manually
before having a coffee break.

Xautolock will typically be used to lock the screen but it really
doesn't care what program you make it start. The only real assumption
made by xautolock is that a new countdown starts as soon as the
locker exits.

One suggested use of autolock is like this:
        xautolock -time 10 -locker xlock