X lock screen

xscreensaver :

• run in normal user

install

# apt-get install xscreensaver

run xscreensaver

$ vi .xinitrc

$ xscreensaver -nosplash &

lock screen

$ xscreensaver-command -lock

slock : 

• minimal screen locker

• type your password directly 

# apt-get install suckless-tools

$ slock

References :
lock screen in wmii (Page 1) / Applications & Desktop Environments / Arch Linux Forums
DWM auto lock after inactivity (Page 1) / Applications & Desktop Environments / Arch Linux Forums