Android: exitOnClose

app.js

var win1 = Ti.UI.createWindow({
	backgroundColor : 'white',
	fullscreen: true,
	exitOnClose: true
});

var button = Ti.UI.createButton({
	title : 'Open',
	width : 150,
	height : 40,
	top : 20
});
win1.add(button);

button.addEventListener('click', function() {
	var win2 = Ti.UI.createWindow({
		backgroundColor: 'blue'
	});
	win2.open();
	win2.addEventListener('android:back', function(e){
		win1.close();
	});
});

win1.open();