I'm in the process of setting up a laptop running Debian Jesse with xmonad as the display manager. I use xmobar to display information about the current state of the system, including the battery level. However, I find that I forget to check regularly and I'm always surprised when my computer suddenly shuts off because the battery died --- I miss the pop-up notifications that I used to get with XFCE.
What can I use to get an attention-grabbing warning about my low battery? Most solutions I've found use dzen, or just display a number on the status bar, which I've found to be insufficient.