Caffeine

If you have problems with your Windows PC locking or going to sleep, the Caffeine desktop app will keep it awake. It works by simulating a keypress once every 59 seconds, so your machine thinks you're still working at the keyboard, so you won't lock the screen or activate the screensaver.

The icon is shown above - it's the leftmost one in the task tray, and this is all you see. Double-clicking the icon empties the coffee pot (that's what the icon is) and temporarily disables the program. Double-clicking it again refills the pot and will keep your machine awake.

By default, the app starts enabled and works every 59 seconds. There are some command-line switches you can use to alter this behavior:

• xx - where xx is a number which sets the number of seconds between simulated keypresses. This must be the first text on the command-line
• -startoff - application starts disabled.
• -exitafter:xx - the application will terminate after xx minutes
• -activefor:xx - the application will become inactive after xx minutes
• -inactivefor:xx - the application will become active after xx minutes
• -appexit - terminates current running instance of the application
• -appon - makes the currently running instance of the application active
• -appoff - makes the currently running instance of the application inactive
• -apptoggle - toggles the running state of the currently running instance of the application
• -apptoggleshowdlg - toggles the running state, and shows a dialog
• -replace - closes the currently running instance, replacing it
• -noicon - does not show a task tray icon
• -useshift - simulate the shift key instead of F15
• -showdlg - shows a dialog indicating whether caffeine is active
• -ontaskbar - show a taskbar button (use with -showdlg)
• -allowss - prevent sleep, but allow the screensaver to start
• -key:xx - simulate using virtual key code xx
•   Note: the codes on the linked page are in Hex, convert them to decimal for use with this parameter
• -keypress - simulate a full keypress, not just a key up event
• -oldicons - use more colorful tray icons
• -darkicons - use icons which work better for dark-on-light color schemes

Caffeine by Zhorn Software works by simulating an F15 key up event every 59 seconds. Of all the keypresses available, F15 is probably the least intrusive, and least likely to interfere with your work.

However, Caffeine might interfere with some apps:

• PowerPoint uses the F15 keypress to pause a video in a slide
• Google Docs/Sheets
• Terminal emulation, e.g. Putty