I have been searching the internet wildly for an answer to this question.
We are creating custom android app for internal use only and we would be installing that on custom andoid devices. We would like to have full control of the device through the app. The end user of this device is not meant to use anything other than the app on this device. I have sealed out all the possibilities of getting out of the app except this one possibility where the program tries to update itself and asks for user permission.
Let me repeat again, This app is not meant to be put on market, only for use with custom devices designed for specific purpose. So security is not an issue here.
The device is rooted and we have done a lot of alterations with it. But I cant quite figure out how to make this update work.
If you have any ideas/solution please share it with me. I can do anything with my device, (even dig a hole in it if required :P) as they would be custom made, and would be packaged with us before going out. Just have to make it work.
If you are talking about internally installing the APK with like an update application specifically designed to update your other application which is not managed by Google Play you may want to look into this. So between xjaphx’s answer and the link I just shared you will be able to install and maintain updates.