Subscribe in a readerAndroid 1.5 introduced a number of new features that application developers can take advantage of, like virtual input devices and speech recognition. As a developer, you need to be aware of backward compatibility issues on older devices—do you want to allow your application to run on all devices, or just those running newer software? In some cases it will be useful to employ the newer APIs on devices that support them, while continuing to support older devices.
If the use of a new API is integral to the program—perhaps you need to record video—you should add a manifest entry to ensure your app won't be installed on older devices. For example, if you require APIs added in 1.5, you would specify 3 as the minimum SDK version:
Source: Android Developers Blog
