That smartphone you carry around with you is an amazing little device.

It is a computer that is the equal of supercomputers of not so long ago. A tweaked Motorola Droid can hit a speed 15 times faster than the computing chips used in the 1979 Cray-1 supercomputer.

It is a telephone and a GPS device and a still and video camera.

But there's another capability not so often discussed: A smartphone can measure its position in space and how fast it is moving and then perform functions based on that information.

It does this using a built-in accelerometer.

There is a long list of different kinds of accelerometers that work in different ways. But they all do one basic thing: measure acceleration -- the rate of change in speed.

The breakthrough for mobile came when accelerometers were made small enough to be a chip on a motherboard.

Forces measured by an accelerometer can be static -- like the constant force of gravity pulling at your feet -- or they can be dynamic -- caused by moving or vibrating the accelerometer. By measuring the amount of static acceleration because of gravity, you can find the angle at which the device is tilted vis-a-vis the Earth. By sensing the dynamic acceleration amount, you can analyze the way the device is moving or when it stops.

Those seemingly simple measurements can have many different and surprising uses. The most obvious use in a cell phone is to change the orientation of the screen when rotating it.

When holding the phone "upright," the accelerometer senses this and tells the phone to display in portrait mode. Portrait mode is good for looking at Web pages. When the phone is held "sideways," the device is told to display in landscape mode. Landscape mode is good for watching video.

An early use of motion detection was seen in laptop computers. The accelerometer in some laptops would detect when the device was in free fall, and it would lock the head on the hard drive, preventing the head from crashing into the disk and destroying the drive and its data.

Accelerometers can also tell when acceleration has stopped suddenly -- you've crashed.

Auto manufacturers use them for telling your car when to deploy its air bags. They detect the rapid decrease in acceleration of the vehicle to determine when a collision has occurred and the severity of the collision.

Automatic Collision Notification systems use accelerometers to call for help when a vehicle crashes in systems like Onstar. Many accelerometer-equipped smartphones have software available for download that mimics the function of an Onstar system. (see my-911.com.)

Nintendo's Wii video game console system is controlled by a Wii Remote that has a sophisticated three-axis accelerometer.

The same idea turns smartphones into game controllers by sensing movement and tilt of the phone and feeding data to the game running on the phone.

The accelerometer in a phone can be used to eliminate blur caused by moving the camera in still pictures and for image stabilization in video by eliminating "shake." Still cameras hold off snapping the "shutter" when the camera is moving. When it's still, the picture is "snapped."

Some digital cameras contain accelerometers to determine the orientation of the photo being taken and for rotating the current picture when viewing.

Since most smartphones and tablets now routinely contain accelerometers, their unique capabilities will start to pop up in more applications and even in computer peripherals.

The Jawbone Era is one of the first Bluetooth headsets to contain an accelerometer. It allows the user to answer phone calls by just touching the headset and to pair the device with another Bluetooth device by shaking. Further motion applications are promised in future updates.

Of the burgeoning ways we can communicate with our devices, motion is becoming an important one.

First Published: November 20, 2011, 5:00 a.m.