ACPI questions about press power button

[dave jones]

Hello,

I'm running FreeBSD 8 on my desktop. I want to write a file or do something
when I or someone presses power button. In devd.conf, I added the
following lines
for testing:

  notify 10 {
            match "system"          "ACPI";
            match "subsystem"      "Button";
            matcho "notify"            "0x00"
            action "echo hello world";
    };

But it doesn't work. Would anyone tell me how to do? Thanks.

Regards,
Dave.