The biometric daemon was proposed in a 2008 paper (PDF) by Pam Briggs and Patrick Oliver, and it's a very clever thought-experiment for a user-centered, adaptive authentication system. The idea is that the daemon, a cuddly toy, (the name is inspired by the Philip Pullman Dark Materials novels) knows a bunch of your biometrics (fingerprints, voice, gait, etc), and uses them to verify your identity before logging you into various services (ATMs, online services, mobile phones).
The daemon learns about your usage patterns -- where and when you go places, what you do there -- and when you do stuff that appears anomalous, you have to "reassure" it by providing additional biometrics and verification. It essentially moves the stuff that your bank already does (annoyingly cutting off your ATM card if you go on holiday because they assume it's been stolen and taken out of the country) to a device that you control, keeping your data with you. It uses the tendency to anthropomorphizing inanimate objects to give users hints for navigating difficult situations.
I can think of several problems with the system: how to recover passwords after your daemon is lost or stolen; what to do when you and your daemon are upset (because you've missed your flight and you need your daemon to log you into your mobile phone so you can call the airlines, but it won't be reassured because you're too tense to properly authenticate), and so on -- but it's an incredibly neat, clever idea, and one that's got me thinking.
Biometric Daemons: Authentication via electronic pets (PDF) (Thanks, Pam!)
I write books. My latest is a YA science fiction novel called Homeland (it's the sequel to Little Brother). More books: Rapture of the Nerds (a novel, with Charlie Stross); With a Little Help (short stories); and The Great Big Beautiful Tomorrow (novella and nonfic). I speak all over the place and I tweet and tumble, too.