If this is a boring flat rectangle, I think take-up will be slow. If a clever designer makes an attractive ‘badge of honour' lapel pin though…
a bluetooth contact tracing ‘CovidCard’…
people only have to carry the CovidCard and don’t have to download or scan anything.

The concept of a self-contained, bluetooth contract-tracing device is a cleaver idea, though. The Aus government is having trouble getting people to download their Covid app, mainly for concerns around privacy, but also requiring iPhone users to have their app running in the foreground to be effective (the app predates Apples + Google's "contact tracing" API).
Allowing people to get a device like this, that they can put in the wallets or on their keys, could help with that. Just need to get people to remember to charge it before they go out.

@lmika Ohhh, I'd completely not thought about charging. We have an app that scans QR codes. It works easily BUT: not enough businesses display the codes AND there are competing QR codes from other non-government apps. One day I tried 5 times to scan only to then realise it wasn't the government QR code…

Huh, that’s interesting. I did hear about the QR code setup, but I didn’t know that there were a bunch of competing apps that use it. I could imagine that getting confusing.
Over here, we just have a register where people write their names and phone numbers before they enter an establishment. I’ve only ever seen it at restaurants and pubs thought, not so much shops or supermarkets.

@lmika Yes, we had to do that at one stage when we were allowed to visit restaurants etc under a degree of shutdown. Now we’re effectively back to normal and can go about our usual daily lives the app and QR code are strongly recommended.

Technically we're no longer doing the registry thing now because we had to shut back down again due to a surge in cases, and all the resturants are closed for anything other than take-away 😅