There was a post recently about a computer that could fit inside of a usb port, little arm chip. It was meant as an open yubikey substitute, but you could easily hide one of those inside of a mass-produced cell phone charger, and suddenly you have something doing arbitrary computation. It didn't have a wireless chip, but on the other hand it was $30, if you made it using off-the-shelf consumer parts. I'm sure an industrial complex would be able to shave the size down and potentially add a wireless chip. Scary stuff.

USB Wifi adapters have been tiny for years, and they have a wireless chip (obviously) and certainly some computation.

Or......there's the $5 wrench

https://xkcd.com/538/

The difference is, if you hit someone with a wrench until they give you the password to some data, they're going not going to continue giving you data. Whereas, if you covertly get access to someone's computer, they're going to keep using it and keep feeding you data.