Invoking some event inside set{}

Question

I have a timer object:

class GameTimer
{
    private CancellationTokenSource cancellation;
    BindingClass bindingClass;
    public GameTimer(BindingClass bindingClass)
    {
        this.bindingClass = bindingClass;
        cancellation = new CancellationTokenSource();
    }
    public void Start()
    {
        bindingClass.SecondsElapsed = 20;
        CancellationTokenSource cts = cancellation;
        Device.StartTimer(new TimeSpan(0, 0, 1), () =>
        {
            if (cts.IsCancellationRequested) return false;
            if (bindingClass.SecondsElapsed > 0)
            {
                bindingClass.SecondsElapsed--;
            }
            return true;
        });
    }
    public void Stop()
    {
        Interlocked.Exchange(ref this.cancellation, new CancellationTokenSource()).Cancel();
    }
}

Another object that holds some variables:

public class BindingClass : INotifyPropertyChanged
{
    private int _secondsElapsed;
    public int SecondsElapsed
    {
        get { return _secondsElapsed; }
        set
        {
            if (_secondsElapsed != value)
            {
                _secondsElapsed = value;
                OnPropertyChanged();
            }
        }
    }
    public event PropertyChangedEventHandler PropertyChanged;
    public void OnPropertyChanged([CallerMemberName] string name = "")
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(name));
    }
}

And a main page:

public partial class GamePage : ContentPage
{
    private int currentSelector;
    private int selectorCount = 0;
    TapGestureRecognizer tapGestureRecognizer = new TapGestureRecognizer();
    Image img;
    BindingClass bindingClass;
    GameTimer gameTimer;
    public GamePage(BindingClass bindingClass)
    {
        InitializeComponent();
        this.bindingClass = bindingClass;
        gameTimer = new GameTimer(bindingClass);
        gameTimer.Start();
        this.BindingContext = this.bindingClass;
        NavigationPage.SetHasNavigationBar(this, false);
    }
}

What would be the proper to display some sort of alert or at least some event, like after the SecondsElapsed reaches 0? I tried putting a DisplayAlert inside set{}, but it does not show any pop-up:

public class BindingClass : INotifyPropertyChanged
{
    private static Page page = new Page();
    private int _secondsElapsed;
    public int SecondsElapsed
    {
        get { return _secondsElapsed; }
        set
        {
            if (_secondsElapsed == 0)
            {
                page.DisplayAlert("AW", "AW", "AW");
            }
            if (_secondsElapsed != value)
            {
                _secondsElapsed = value;
                OnPropertyChanged();
            }
        }
    }
    public event PropertyChangedEventHandler PropertyChanged;
    public void OnPropertyChanged([CallerMemberName] string name = "")
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(name));
    }
}

I don't know if I can call some functions or fire some event inside BindingClass.