Dallas Semiconductor iButton
One of these popped up for $25 and I've been wanting one for years so I bought it.
This is a Dallas Semiconductor ibutton which Sun has affixed to a ring, they were supposed to be highly durable and potentially purvasive hardware authentication tokens. Par for the course for sun they feature an actual jvm that can run applets and can crypographically authenticate you.
It has many hardware features- a battery, which provides an rtc to prevent backdating authentication fames. They're designed to last ten years on a keychain, they're tamper evident if opened and if you open them anyway a microswitch zeroes out the keys. They also zero out on extreme temperatures and unusual voltage conditions.
The ibuttons are still made though no one ever like made them work as a login token for any common OS, so you're more likely to find one being used as a key for a safe or a forklift.