When network is being actively used, a notification with numerical status-bar indicator will show up and constantly update itself. The indicator will be hidden if network is idle, but you can still find all the statistics in the notification panel.
New version 2.0 brings per-app insights
Besides the overall usage, a new application-level usage statistics is added in verison 2.0! App recently consuming network traffic will be shown directly on the notification. On Android 4.1+, a list of recent traffic consuming apps is included in the expanded notification.
* Light-weight focused implementation in extremely low footprint. Start-on-demand background service for only 3M approximately (vary with devices and Android versions)
* Absolutely ZERO memory and battery consumption when network is inactive.
* Hide status-bar indicator when network is not being actively used.
* Selectively monitor only cellular (mobile network) data traffic or all network traffic.
* Per-app usage statistics within expandable notification. (expandable only on Android 4.1+)
* Minor traffic (sensitivity configurable) will not be notified.
* Click the notification to reset the traffic statistics (on Android pre-4.1) or additional actions on notification for quick reset and settings (on Android 4.1+).
* Fixed per-app stats in Android 4.3.
* Fixed a rare crash reported by users.
* Minor improvements.
* No longer need "package update" receiver on Android 3.1+, for slightly improved device experience.