Yup. You can always keep it powered off and in a Faraday sleeve until it's time to use it at the border. It should be possible to distribute a device that's smaller and lighter than a passport, and I'd be all for it, so long as it's at least as reliable and/or if there's a fallback process when it isn't.

I like my RSA fob, they changed the app name one day and I wasted time working with the IT department.