this is a Dallas Semiconductor ibutton which they have 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 which run applets with can crypographically authentice 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 linux or whatever, so you're more likely to find one being used as a key for a safe or a forklift.