detect barcode scanner from web browser

In a Java EE web application, I need to read data from barc开发者_如何学运维ode scanner(connected to the user's machine - client side),display the data in a textbos and send the code back to the server.I think I understood how to do it.

Is it possible to detect whether the scanner is connected/turned on and if not, display a warning in the web page that the scanner is not connected? (using some activex controls or any other method)

When I did this I simply used a textfield to capture the input from the scanner. Why do you need to detect the scanner?