Software to alert when caps lock is on

Solution 1:

As of 18.04 —when Ubuntu moved to Gnome— you'll want the Lock Keys extension.

The 1 A light up if numlock and capslock are on. Click the indicator to turn them on.

There's a PPA for indicator-keylock that does this.

sudo add-apt-repository ppa:tsbarnes/indicator-keylock
sudo apt-get update
sudo apt-get install indicator-keylock

For KDE users, there's KeyLeds, Xfce has kbdleds and gnome3 has Lock Keys

Solution 2:

http://www.maketecheasier.com/10-must-have-indicator-applets-for-ubuntu-12-04/2012/06/15

Key Lock Indicator :

Not all laptops come with a Caps lock or Num lock indicator or even button and this is why this indicator becomes necessary to know whether or not caps lock is on or not. It notifies every time there is a change in the state of the key. By default, it pops in panel when the locks are turned on but it can be configured to always stay in panel even when locks are off. This applet needs a restart to reflect the changes for the first time.

Ubuntu-Applet-Keylock To install Key Lock:

sudo add-apt-repository ppa:tsbarnes/indicator-keylock
sudo apt-get update
sudo apt-get install indicator-keylock