procedure TForm1.Button1Click(Sender: TObject);
var
 lpDisplayDevice: TDisplayDevice;
 dwFlags: DWORD;
 cc: DWORD;
begin
 lpDisplayDevice.cb := sizeof(lpDisplayDevice);
 dwFlags := 0;
 cc:= 0;
 while EnumDisplayDevices(nil, cc, lpDisplayDevice , dwFlags) do
 begin
 Inc(cc);
 memo1.lines.add(lpDisplayDevice.DeviceString);
 {there is also additional information in lpDisplayDevice}
 end;
end;