police car listening to avatars hud

im trying to script up a hud to a police car i made, here is how it is in my head

avatar sits in car
car begins to listen
avatar "on" the seat presses a hud button
lights turn on/off ect
avatar gets out
car stops listing to avatar on seat

but the hud dosent wont to work anyone have any idea how to make it work for a hud that the avatar is wearing?

integer hanndle;

changed(integer change)
    {
        if (change & CHANGED_LINK)
        {
            key agent = llAvatarOnSitTarget();
            if (agent)
            {
                if(llSameGroup(llDetectedKey(0)) == TRUE)
                {
                    hanndle = llListen(0,"","",""); 
                }
                else
                {
                    llUnSit(llAvatarOnSitTarget()); 
            }
        }
        else
        {
                    llListenRemove(hanndle);
                }
        }
    }
    listen(integer channel, string name, key id, string message)
    {
        if (llAvatarOnSitTarget()) // how to make it listen to avatar on sittargets hud
        {
            if(message == "lightson")
            {
                llMessageLinked(LINK_ALL_CHILDREN, 0,"lightson", "");
            }
            else if(message == "lightsoff")
            {
                llMessageLinked(LINK_ALL_CHILDREN, 0,"lightsoff", "");
            }
        }
    }

Please see notes on the use of llGetOwnerKey() in the thread /54/b4/257817/1.html