Laptop Mode Tools
From ArchWiki
The Linux kernel, starting from version 2.6.6, contains a feature called laptop mode. This feature is also present in the Linux 2.4 series starting from version 2.4.23. When you enable this feature, The kernel allows your hard drive to spin down more often, resulting in significant power savings. To make laptop mode work, you need to install some scripts and configure some things. The Laptop Mode Tools package contains everything you need to make laptop mode work. Laptop Mode Tools Website)
To install laptop-mode-tools:
pacman -S laptop-mode-tools
Add laptop-mode to your DAEMONS array in /etc/rc.conf:
DAEMONS=(@network @acpid @syslog-ng @alsa @hal @fam @laptop-mode)
Be sure to go through the config files, in /etc/laptop-mode/laptop-mode.conf and /etc/laptop-mode.conf/conf.d/*, as many powersaving features are not enabled by default.
More tips and information are available on the Laptop page of this wiki.