How can I watch an address on Windows and Android? I want to be informed of transactions of my Bitcoin address on the Windows and the Android app. Can I use the same Bitcoin address on both? If yes, how can I backup the address on Windows and restore it on Android?
Just use bitcoind 
-walletnotify=    Execute command when a wallet transaction changes (%s in cmd is replaced by TxID)

in a script or for more details, access the bitcoind API via RPC  https://en.bitcoin.it/wiki/Original_Bitcoin_client/API_calls_list