Google first implemented face-unlock in ICS, and since then, it's been hard at work improving the feature and acquiring new IP related to it. Last fall, the search giant patented a way for multiple users to use face-unlock on a single device. This week it obtained a new patent for a method that requires users to make a series of facial expressions to gain access to a system. Essentially, the patent claims a method where a device captures two images of a user, then compares the differences in the images to identify a facial gesture and authenticate the user.

In other words, its a face-unlock method where a device looks at two pictures of your mug to tell if you're raising an eyebrow, frowning or sticking your tongue out as instructed by a prompt from the device. And, it double checks to ensure that it is, in fact, the same face in both images. Oh, and the patent leaves room for a series of expressions to be used -- so at some point in the future, you may have to give your Google-fied phone a wink and a smile before it grants you access. Guess that's easier than remembering a PIN, right?