Google is in the process of selling parts of Motorola to China's Lenovo, but not all of it. It's not selling Motorola's visionary research group, Advanced Technology and Projects (ATAP), for example.

Reports that mention Google's ATAP group typically list a few of the better-known and more colorful projects they're working on.

One of these is Project Ara, which is a modular phone concept that enables people to use 3D printers and other hacks to build just about any kind of phone they want. Google recently announced hardware-hacking conferences for the project that will begin in April. Some say the phone could go on sale as early as next year for as little as $50. Wow! Cool!

Another is a pill called a "vitamin authentication pill" that generates a password when swallowed. Uh, OK. That sounds, er, interesting.

The company is also working on electronic tattoos. Wait a minute -- electronic tattoos? That makes no sense. How can a tattoo be electronic?

Electronic tattoos sound ultra-futuristic -- something in the realm of transport beams, Martian terraforming and cheap iPhones.

Here's what everybody needs to know about electronic tattoos: They make perfect sense; they're inevitable; and they're going to be on the market very soon. In fact, it's almost certain that you'll at least try one within the next five years.

What is an electronic tattoo?

First, let me tell you what they're not: They're not tattoos. There's no ink, needles or piercing of the skin.

The reason they're called "tattoos" is that their application is similar to those in children's fake tattoos. It usually starts out on a sheet of plastic, is then applied to the skin and rubbed on from outside the plastic, then the plastic is peeled away, leaving only a very thin, rubber patch that has a layer of flexible silicon wires.

The concept behind electronic tattoos is simple. The idea is to create an electronic device, usually involving sensors, that is thinner than a sheet of paper and as flexible as a Band-Aid that can stick to the skin.

The secret sauce is flexible electronics. The core benefit is that they become part of the body in a non-invasive, painless and relatively inexpensive way.

In addition to sensors, the electronics package can contain wireless networking capability, so they can not only convey sensor data easily, but also be controlled from a remote computer or smartphone.

Why are electronic tattoos happening now?

Almost every big technology revolution is preceded by a materials revolution. For example, the computer revolution owes its trajectory to the development of semiconductor materials, including silicon, which replaced vacuum tubes and brought into existence Moore's Law, the law that states the number of transistors on integrated circuits doubles roughly every two years.