How often has it happened that you have inadvertently hit the Caps Lock key and continued to type … ??? 

In Windows 7, you can set it hear a warning tone when you press the Caps Lock, Num Lock or Scroll Lock keys.

Open Control Panel > Ease of Access Center > Make the keyboard easier to use

Check the Turn on Toggle Keys checkbox.

Click Apply > OK.

Now you will hear a tone when you press Caps Lock, Num Lock or Scroll Lock.

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