I bought this a few years ago and tried it a couple of times, but it just ended up being inconvenient, so I'm selling it. How to use it: You register it for two-factor authentication with your Google account, and then press the button when you need to authenticate. In preparation for listing it, I confirmed that it can be charged with a USB cable and that the indicator blinks when the button is pressed. I hope someone can find a use for it.