You're missing a very important limiting factor: battery life. You can't fit a lot of battery in the space of a credit card, and you can't exactly count on unwitting carriers to properly recharge and maintain them.

Given those constraints, practical applications would be severely limited. As the article mentions, it's probably undercover personnel who are carrying these. The power budget would likely rule out remote access or remote streaming. I'm guessing these credit card snitches are little more than local audio/video recorders with very limited run time.

You'd be very surprised just how little energy a radio can get away with. We're talking energy scales where ambient radio waves are a viable source of power.

It's totally viable to have a device like this with an essentially infinite battery life. You have to compromise on audio quality, recording time, and upload rate, but you can. It's not even anything particularly crazy or difficult.

The more practical way is a remote power supply. You can get a small amount of power at a good distance with radio. Just enough to keep the recorder ticking and to charge a capacitor for transmit bursts.