acpid binary package in Ubuntu Precise i386

 Modern computers support the Advanced Configuration and Power Interface (ACPI)
 to allow intelligent power management on your system and to query battery and
 configuration status.
 .
 ACPID is a completely flexible, totally extensible daemon for delivering
 ACPI events. It listens on netlink interface (or on the deprecated file
 /proc/acpi/event), and when an event occurs, executes programs to handle the
 event. The programs it executes are configured through a set of configuration
 files, which can be dropped into place by packages or by the admin.

Source package