Why can't smartmontools disable SMART check?

[Ooker]

When I use smartctl -s off /dev/sda with admin privilege, the SMART support is said to be disable:

    C:\Program Files\smartmontools\bin>smartctl -s off /dev/sda
    smartctl 6.5 2016-05-07 r4318 [i686-w64-mingw32-win8.1] (sf-6.5-1)
    Copyright (C) 2002-16, Bruce Allen, Christian Franke, www.smartmontools.org
    
    === START OF ENABLE/DISABLE COMMANDS SECTION ===
    SMART Disabled. Use option -s with argument 'on' to enable it.

It is confirmed by using smartctl -a /dev/sda/:

    C:\Program Files\smartmontools\bin>smartctl -a /dev/sda
    smartctl 6.5 2016-05-07 r4318 [i686-w64-mingw32-win8.1] (sf-6.5-1)
    Copyright (C) 2002-16, Bruce Allen, Christian Franke, www.smartmontools.org
    
    === START OF INFORMATION SECTION ===
    Model Family:     Hitachi/HGST Travelstar Z5K320
    Device Model:     Hitachi HTS543232A7A384
    Serial Number:    E2034243EEG7TP
    LU WWN Device Id: 5 000cca 690e24d54
    Firmware Version: ES2OA60W
    User Capacity:    320,072,933,376 bytes [320 GB]
    Sector Size:      512 bytes logical/physical
    Rotation Rate:    5400 rpm
    Form Factor:      2.5 inches
    Device is:        In smartctl database [for details use: -P show]
    ATA Version is:   ATA8-ACS T13/1699-D revision 6
    SATA Version is:  SATA 2.6, 3.0 Gb/s
    Local Time is:    Tue Jan 17 23:10:55 2017 SEAST
    SMART support is: Available - device has SMART capability.
    SMART support is: Disabled
    
    SMART Disabled. Use option -s with argument 'on' to enable it.

But when I restart my computer, the SMART check comes back again. Why is that?

My BIOS version is ​1.31, and there is no SMART option in it (only D2D recovery).

^{I have asked this question on ​Super User as well.}

[Christian Franke]

Even a BIOS without a corresponding setting may enable and check SMART on reboot.

PS: This is a bug tracker, not a support forum. For future support questions, please use the smartmontools-support mailing list instead.