how to trigger button click using keyboard enter key?

<asp:Panel ID="Panel2" runat="server" DefaultButton="Button1"> <asp:TextBox ID="TextBoxcityandstatesearch" runat="server" Height="26px" Width="251px" ForeColor = "Gray"></asp:TextBox> <asp:Button ID="Button1" runat="server" Text="Search City, State" Font-Names="Arial" ForeColor="#3737FF" Height="33px" Width="140px" onclick="Button1_Click" /> </asp:Panel> I have a search textbox and search button, the search textbox allows user to input text. after user inputs text, the button click can be triggerred by press enter key on keyboard, becuase we have set panel2 and used defaultButton as Button1. However, we have built auto fill in feature for text box. When user type 3 letters, it shows a list of option. so it is v ...