How do I find out what apps are using data?

I have a Galaxy S4 running Jelly Bean 4.

2. I was getting about 6GB per month on the old SIM card, so I want to figure out what apps are using data.

The phone came with a "My Data" widget on the home screen, but I couldn't find any way to get at it, or even any way to see what apps are using data. Does anyone know how to do this? Thanks! Just to be clear, the widget you're referring to is not part of the stock Android build, but rather an app from the Android Market. You can still find it by searching for "my data", but I believe it's no longer in the Android Market, so you'd need to use the APK link if you want to install it manually.

However, if you go into Settings > More > Data Usage, you should see a screen showing you all of the apps that are currently using data, including apps that are not installed on the device. You can also switch to the "App history" tab and look at the list of all of the apps that have been recently used.

If you go to Settings > More > Data Usage, you should see a screen showing you all of the apps that are currently using data, including apps that are not installed on the device. I don't think you can see what apps are using data unless you are rooted, but you can see the usage by app from the list in Settings > More > Data Usage. Just tap the Menu button and select "Manage apps". From there you can delete apps that are using too much data.

How do I control app data usage on iPhone?

I have a very old iPhone (4). It's not jailbroken. It is on iOS 7. When I go to the App Store and select "Apps" it says "1.3 GB". I don't understand what that means, and I don't want to continue installing apps if there is data usage. How can I get a better idea of how much data I'm using?

IOS devices have a fixed amount of data (at least for now). Apps cannot be denied from accessing data or even throttle your usage. The system will attempt to provide some level of notification when your data runs low. There is no control over this other than removing apps that are using the data.

So, if you have some apps that you can't do without, you're going to have to suffer through the data being used up. There's no way to control your iPhone's data usage. But you can control your data plan.

Go to your cellular settings, and switch from "data only" to "data & cellular". If you want to limit your data usage, but you want to keep your cellular phone working, I would recommend switching to the "data only" option, which is less expensive.

Is there a way to track app usage on iPhone?

I mean, I'm a developer, and I would like to have access to my app usage.

There's no way to do it directly. However, you can use the iTunes Connect APIs to download your app's usage history (there are 4 different types of usage - daily, weekly, monthly, and yearly).

If you'd like to use this data for internal purposes, you can have your own server which will query the iTunes Connect API using your own application key. There is also a limit of 1 GB per day, so if your app is storing too much information, you'll need to delete older data (or just add a "freshen" button).