I have two divs with the same ng-controller in AngularJS, how can I make them share information?

I have two different div tags in my html code referencing the same controller in AngularJS. What I suspect is that since these divs aren't nested they each have their own instance of the controller, thus the data is different in both.

<div ng-controller="AlertCtrl">
<ul>
    <li ng-repeat="alert in alerts">
        <div class="span4">{{alert.msg}}</div>
    </li>
</ul>
</div>        
<div ng-controller="AlertCtrl">
<form ng-submit="addAlert()">
    <button type="submit" class="btn">Add Alert</button>
</form>
</div>

I know this could easily be fixed by including the button in the first div but I feel this is a really clean and simple example to convey what I am trying to achieve. If we were to push the button and add another object to our alerts array the change will not be reflected in the first div.

function AlertCtrl($scope) {

$scope.alerts = [{
    type: 'error',
    msg: 'Oh snap! Change a few things up and try submitting again.'
}, {
    type: 'success',
    msg: 'Well done! You successfully read this important alert message.'
}];

$scope.addAlert = function() {
    $scope.alerts.push({
        type: 'sucess',
        msg: "Another alert!"
    });
};
}