Trusty: Caffeine doesn't appear in panel after update

The 2.7 release removes the user interface and manual operation. Caffeine is now fully automatic: When the active window is full screen, Caffeine inhibits desktop idleness.

This has been changed in version 2.8 (released January 15th, 2015), which has:

• a caffeine program that works as v2.7: desktop idleness is prevented for full screen applications – fully automatic with no UI;
• a caffeine-indicator program that works as v2.6 and earlier: an icon is shown in the panel that enables/disables desktop idleness;
• a command caffeinate, that prevents desktop idleness for the duration of a command, e.g. caffeinate steam will prevent the screen saver while steam is running.

As this answer states, Caffeine 2.6 and up is fully automatic depending on if your window is fullscreen. The developers removed the manual toggle in the menu bar.

A new fork made by mildmojo called Caffeine Plus brings the manual toggle with the icon in the menu bar back. You can install it manually with the .deb file or via PPA:

sudo add-apt-repository ppa:nilarimogard/webupd8
sudo apt-get update
sudo apt-get install caffeine-plus

Fallback to version 2.6 by using another ppa for now. A request to enable the toggle functionality has been made.

sudo apt-get purge caffeine && sudo apt-get autoremove
sudo add-apt-repository --remove ppa:caffeine-developers/ppa
sudo add-apt-repository ppa:behda/ppa
sudo apt-get update && sudo apt-get install caffeine

If it does not work then try following solution.

1. Install Caffeine from behda ppa. This will resolve dependencies and configure/installs icons, shortcuts...

2. Get the source file:

   tar -xzvf caffeine_2.6.2.tar.gz -C /path/to/preferred/dir
   

3. Test:

   cd /path/to/caffeine/dir
   ./bin/caffeine
   

4. Change startup executable on /usr/share/applications/caffeine.desktop