Have you ever been to the beach? Did you
see a man with a headset pointing a long pole
at the ground? If so you might have seen a
person using a metal detector. People use
these devices to find metal.
Metal detectors make magnetic waves. These
waves go through the ground. The waves
change when they hit metal. Then the device
beeps. This lets the person with the device
know that metal is close.
The first metal detectors were meant to help
miners. They were big. They cost a lot of
money. They used a lot of power. And worst
of all, they didn't work well. People kept
trying to make them better.
Metal detectors got smaller. Now they are
light and cheap. They also work better. That
is why people bring them to the beach. They
can look for rings in the water. They can
look for phones in the sand. Metal detectors
help them find these things. They usually just
find junk though.
Metal detectors also protect people. They
help to keep guns out of some places. They
are in airports. They are in courthouses.
Some schools use them. They help guards
look for weapons. Guards use special wands
to find metal on a person.