Notifications to all devices to update state

A device state service supported on an application server is disclosed herein. The device state service is configured to dynamically monitor a device state across devices, and particularly monitor whether or not a device is currently active (e.g., incoming or outgoing ringing, incoming or outgoing busy signal, audio and/or video call in progress, etc.) The active device transmits device state data along with context data and sensor data (collectively "real-time data"). The inactive (or subject) devices may likewise transmit real-time data to the device state service. The device state service determines an action for the subject and/or active devices to perform based on the received real-time data. For example, when a user's smartphone is currently active (e.g., a call in-progress), the user's tablet may enter a power save mode to save resources.