This is my build of suckless's slock. Their original readme is below...
simple screen locker utility for X.
In order to build slock you need the Xlib header files.
Edit config.mk to match your local setup (slock is installed into the /usr/local namespace by default).
Afterwards enter the following command to build and install slock (if necessary as root):
make clean install
Simply invoke the 'slock' command. To get out of it, enter your password.