diff --git a/hgdriver/hgdev/hg_scanner.cpp b/hgdriver/hgdev/hg_scanner.cpp
index a80ea1f..1d54eda 100644
--- a/hgdriver/hgdev/hg_scanner.cpp
+++ b/hgdriver/hgdev/hg_scanner.cpp
@@ -3640,6 +3640,9 @@ int hg_scanner::device_io_control(unsigned long code, void* data, unsigned* len)
 	}
 	else if(code == IO_CTRL_CODE_GET_SERIAL)
 	{
+		if (!is_online())
+			return SCANNER_ERR_DEVICE_NOT_FOUND;
+
 		std::string ser = get_serial_num();
 		if (*len < ser.size() + 1)
 		{