Nearly all of computer security boils down to one question: How can a device know that you are you?
Passwords are the most basic tactic for confirming your identity. If you can come up with your secret string of numbers and letters, you must be you.
But everyone knows that passwords are pretty weak barriers, in part because people are bad at choosing them (tending to use innovative combinations such as "password" and "123456") and because computers are good at breaking them.
Other than passwords, there are a host of other tricks, all with that same goal in mind: verifying that you are you. Two of the most common are security questions (silliness) and two-step verification such as Gmail's, which involves a secondary code that only you have access to.
These, however, are all variations on a theme -- logging in, account by account, to the data or service you are trying to access. A new device called the Nymi has a different idea in mind for how to verify your identity, and with it, its creator Bionym prefigures a time where you don't so much as log in as present yourself.
What is this device? It's a little bracelet you wear that makes sure you are you by verifying your unique heartbeat. It then can unlock your accounts and devices, just by its presence. If someone else wears the device, no dice. (Rumors of a similar Apple device have circulated for years.)