This shell script will send you a push notification if there are new Gentoo updates available. It's based on ftf's Ruby script for Prowl.
To get the Application token just create a new application on the Pushover website: https://pushover.net/apps/build.
The "User Key" is displayed on your user profile.
Add this cronjob and make sure the user has permissions to run the emerge command:
0 20 * * * /bin/zsh /root/tools/updatecheck.sh >/dev/null 2>&1