Do something for someone on touch Once and Once only

list before;
default
{
    touch_start(integer total_number)
    {
        if(llListFindList(before,[llDetectedKey(0)]) != -1)
        {
           llSay(0,"Youve already had your free gift!");
        }
         if(llListFindList(before,[llDetectedKey(0)]) == -1)
        {
            before += llDetectedKey(0);
            llSay(0,"Here is your free gift!");
        }
       
        
    }
}