IrssiNotifier uses Google Cloud Messaging (Android push mechanism), so notifications consume very little battery and are almost real time.
Irssi script set up is straightforward and instructions are available at the app's web page at https://irssinotifier.appspot.com.
All messages are end-to-end encrypted with encryption key specified by you, so your privacy will be protected.
If you find IrssiNotifier useful, please consider buying IrssiNotifier+. IrssiNotifier+ is a supporter version that has all the same features than the free version, plus pull mechanism, which allows you to receive IRC hilights even if you're not online all the time. Putting this feature into paid version helps cut down server costs. Thank you for your support!
Check https://irssinotifier.appspot.com for more information. Unofficial scripts for WeeChat and Python are also available. Project is open source and hosted on GitHub.