Demagnetize then remagnetize in the desired direction .

退磁,然后沿预定的方向磁化。

I think they forgot to demagnetize it .

我想他们忘了给它消磁了。

When you rent or buy a dvd the checkout clerk rubs it across a pad to demagnetize the metallic glass so it won 't trigger an alarm when you leave .

当你租或者买dvd光盘时，收银员会把它滑过一个垫子使其中的金属玻璃退磁，所以在你离开的时候不会引起警报。