Pressed the power button and then Hold for 2(or 3,less then 4) seconds to power off the system

hi all, i had read a lots of result in google with the key words "hold power button linux",but found just a little useful info:

When you push the power button, the BIOS is invoked. If you release
> within 4 seconds, the BIOS sends an ACPI event to the running OS,
> telling it that the power button has been pushed.

So i did know it is very default for me to implement this function for my clients' requirements since i'm a newbie in acpi,
but i just want to konw is it possibly to implment this function describe by the subject??

By the way, i had implement the common use of acpi on my NOVA-ATOM board pc with the power button by press it in 4s then the system is poweroff cleanly.

sorry for my pool English...
any help about this will be appreciated
Best Regards.