Passwords suck; if they're short, they're insecure; if they're long, they're hard to remember; if they're hard to remember one is inclined to write them down thus making them insecure; full circle.
One solution is to use password phrases but they have a poor user-experience; no-one enjoys entering long passwords on a mobile device, or anywhere else for that matter.
I imagine a simple device with these properties:
Does such a device (product) exist?
No such security is typically needed but it would be kind of cool to have such a device.