Here's the sample for you where I am hiding Calendar on ESC press
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js"></script>
<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>
<asp:TextBox ID="TextBox1" runat="server" onkeyup="KeyUp(event.keyCode)"></asp:TextBox>
<cc1:CalendarExtender ID="CalendarExtender1" runat="server" TargetControlID="TextBox1"
Format="yyyy-MM-dd" PopupButtonID="ImageButton1">
</cc1:CalendarExtender>
<asp:ImageButton ID="ImageButton1" runat="server" ImageUrl = "~/images/calendar.png"/>
<script type="text/javascript" language="javascript">
function KeyUp(keyCode) {
if (keyCode == 27) {
$find("<%=CalendarExtender1.ClientID %>").hide();
}
}
</script>