Take off the battery cover. Holding the volume-down button, use the stylus to push (the release) the soft reset button. Keep holding the volume down until the 3-color screen shows up. This is called the bootloader. If your phone is already HardSPL'ed, the second line of text on the 3-color screen should have the word "Olinex" at the end of it.
If your phone has had custom ROMs flashed before, it will still be HardSPL'ed, unless your friend purposely re-locked the SPL. In other words, the SPL remains unlocked unless you specifically lock it again.
To get out of the bootloader, just hit the soft reset button again.
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Phone: HTC One X (AT&T version) Rooted, Bootloader Unlocked, S-Off
Tablet: Samsung Galaxy Note 8 (WiFi only) Rooted