Do you like to spend time at the beach? Of course you do! Who doesn't? What do you like to do at the beach? Swim? Sunbathe? Build sand castles?

Did you know that some people like to search for buried treasure on the beach? Have you ever seen someone walking along the beach carrying a long metal stick pointed toward the sand? They may have also been wearing headphones connected to the long metal stick. What were they carrying? A metal detector, of course!

Metal detectors can be used to detect metal objects hiding under the sand. The ultimate score would be a large metal chest filled with long-lost treasure. More likely, though, you'll find coins dropped by beachgoers.

Large metal detectors shaped like doorways or handheld wands are also used in airports and other buildings to help security personnel scan for weapons and other items that could pose a risk to safety. So just how exactly do these things tell what's metal and what isn't?

Most metal detectors produce an audible signal when metal is detected. That's why those people on the beach wear headphones connected to their handheld metal detector units.

Very low frequency technology, also known as VLF or induction balance, is arguably the most popular metal detection technology in use today. VLF technology uses two coils that create an electromagnetic field. When this field encounters an object that conducts electricity, such as metal, the object's own magnetic field is detected. This causes the detector to emit an alert that a metal object has been detected.

Since most metal detectors must detect a metal object's magnetic field, objects need to be fairly close to the surface (within about a foot or so) to be detected by inexpensive metal detectors. More advanced — and expensive — metal detectors can detect things buried much deeper. Advanced metal detectors can also provide information about what types of metals are below the surface.

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