"Postcard" might be a bit of a misnomer too, because it's mentioned that overall "envelopes" weren't being screened, just packages.

Just slip an AirTag in the greeting card and it made it onto the ship, someone opened it, went "WTF" and tossed the AirTag immediately.

Guess they'll x-ray all their inbound envelopes now, too. I'm also given memories of Entertainment Weekly when they shipped a fully functional Android phone (with T-Mobile data!) stripped down between the pages of a magazine ad for the CW Network... all just to display a feed of Tweets. https://mashable.com/archive/ew-has-smartphone-inside#92887I...

Or that time Microsoft included a free hotspot in some magazines.

https://www.pcmag.com/news/microsoft-embeds-wi-fi-routers-in...

There are ultra thin credit card size BT / GPS trackers designed for wallets. https://duckduckgo.com/?q=credit+card+size+gps+tracker&ia=we...

Look at nordic chips. They were super smol even when I was using em almost a decade ago. Wsclp are crazy smol.