Use case:
A Delivery note is created and save, then needs to be prepared. Person in-charged for preparing gets a notification from Todo with a blinker or any physical device that can be used as an alert system. Do any of you know a device or a way to make one that can do this?
Check REST API and your device SDK to understand how you can do this.
Or you can use a message broker, such as https://www.pubnub.com/ or https://www.ably.io/ or setup your own MQTT server to push notifications from ERPNext to any device using hooks. Device choice is yours: android, arduino, Ras pi, etc