Why a Magnet turns the laptop display off?

Question

I remember when I touched the lower left corner of the laptop keyboard with a strong magnet (such as a microwave magnetron), the screen immediately went off (black) and when I removed the magnet it would turn on again.

Unfortunately I cannot provide any further information or documentation as I no longer have access to my old laptop

Why does this happen?

Solution

Because there is a reed switch in the laptop base and a corresponding magnet in the laptop lid. This is used to detect when the laptop is closed and so turn the screen off and potentially put the laptop into standby.

This is quite a common feature in laptops. This also occurs in tablets

Comments

[looooongname]

en.wikipedia.org/wiki/Reed_switch for more info ;-)