When you go through a metaldetector at the airport with a conductor such as keys in your pocket, the alarm goes off.
当你带着一个导体（比如口袋的钥匙）走过机场的金属探测器时，机器会发出警报声。
2
They passed through the metaldetector at the door to their workroom (they pass through it going in and coming out) and walked downstairs to the racks where they had left their bikes.
她们走过设在车间门口的金属检测器（她们出入车间都要被检测），然后再走到楼下她们放自行车的地方。
3
Inspect the stock (or better yet, use a metaldetector) before cutting.