Question to unlock level

Unity Engine
1

I have a menu. I’ve done:
"New Game
Set Level
Exit "

When I press Set Level I flips to another scene (using Application.LoadLevel (n);).
In the Set Level button to go there (Level 2, 3, nothing is fixed.)
"Level 1
Level 2
Level 3. "
/ / / / I use a script

var isl01Btn = false;

function OnMouseUp()
{
        if(isl01Btn)
        {
                Application.LoadLevel(7); ///7 - number of level.

        }
}

Attention question:
How do I get if I pass Level 7, Level 2 to unlock and button worked. As I understand it, it is necessary to prescribe in:

if (isl01Btn   "continued here")

but I do not know how. Help solve this very problem.

Thank you in advance.

PS: Please do not send me to the Player Prefs. Could not understand.

2

P.S.S I am from Russia. Translate through Google Translator. So if you do not understand I’m sorry …

3

So, once you get to level 7, you want to unlock the next level, and make it appear in the menu to be playable?

4

I have the first 7 stages - the menu. From 7 starts the game itself. I have a menu Set Level.
There is knipki to go to other levels. I need to pass at Level 7 Level 8 Set unlocked.