[Browsable(false)]
public List<AlertForm> AlertFormList { get; }

<Browsable(False)>
Public ReadOnly Property AlertFormList As List(Of AlertForm)

using DevExpress.XtraBars.Alerter;

// Displays an alert window.
alertControl1.Show(this, "Alert", "The alert description.");

// Closes all active alert windows.
foreach(AlertForm alert in alertControl1.AlertFormList)
    alert.Close();

// Closes the specified alert window.
AlertForm alertWindow = alertControl1.AlertFormList[0];
if(alertWindow != null)
    alertWindow.Close();

Imports DevExpress.XtraBars.Alerter

' Displays an alert window.
alertControl1.Show(Me, "Alert", "The alert description.")

' Closes all active alert windows.
For Each alert As AlertForm In alertControl1.AlertFormList
    alert.Close()
Next alert

' Closes the specified alert window.
Dim alertWindow As AlertForm = alertControl1.AlertFormList(0)
If alertWindow IsNot Nothing Then
    alertWindow.Close()
End If