IsKeyJustDown(key, newkeys, oldkeys)
{
    if((newkeys & key) && !(oldkeys & key))  return 1;
    return 0;
}

public OnPlayerKeyStateChange(playerid, newkeys, oldkeys)
{
    if(IsKeyJustDown(KEY_NO, newkeys, oldkeys))
    {
        if(GetPlayerState(playerid) != PLAYER_STATE_DRIVER) return 1;
        new engine,lights,alarm,doors,bonnet,boot,objective;
        new vid = GetPlayerVehicleID(playerid);
        GetVehicleParamsEx(vid,engine,lights,alarm,doors,bonnet,boot,objective);
        if(vid != INVALID_VEHICLE_ID)
        {
            if(engine == VEHICLE_PARAMS_ON)
            {
                SetVehicleParamsEx(vid,VEHICLE_PARAMS_OFF,lights,alarm,doors,bonnet,boot,objective);
            }
            else
            {
                SetVehicleParamsEx(vid,VEHICLE_PARAMS_ON,lights,alarm,doors,bonnet,boot,objective);
            }
        }
    }
    return 1;
}