The Android system has a flag called "Unknown Sources" that allows it to install applications from non-market sources.
If I sign my application as described on the android developer website (i.e. with a certificate that is created using the private keys I got from google), and decide not to publish my application on the android market, but host it on my own site.
Will this application be considered a non-market by the android system ? Will it still install with the "Unknown Sources" option turned off ?
"Unknown Sources" allows for the installation of applications via download links (.apk files from the Browser) and has nothing to do with code signing. All applications need to be signed and should be zipalign'd before posting them.
Unlike other platforms (like BlackBerry), the only requirement is that your application be signed using a private key you control or own. I recommend against using keys that are not your own. If you use a private key that other people can obtain, other people can post updates to your application that the system will trust.
The short answer is no, it will not install via your own web site with "Unknown sources" disabled on the device.
Well, technically, anyone could sign an application the same way as you would for the market.
If it's not coming from the Android Market it's an unknown source, unfortunately.
It will be considered a non-market app, and you do have to have "unknown sources" ticked.
来源：https://stackoverflow.com/questions/4947903/signing-an-app-but-not-publishing-on-android-market