Actigraphy is a non-invasive way of monitoring human activities such as rest and movement. Today it is usually a device worn on the wrist that uses an accelerometer to track movements. Examples of todays most common trackers would be Fitbit, Pebble, Garmin, MisFit, Jawbone, etc. This type of sleep tracking is quite limited in both accuracy and abilities, but it can provide a reasonable estimate of overall sleep duration. A significant downside to wrist actigraphy is it cannot accurately measure progressive sleep stages 1,2,3,4 and REM (rapid eye movement).
A sleep clinic is able to load up on laboratory grade sensors and get many meaningful measurements.
Professional sleep clinics use polysomnography,which involves taking multiple measurements including brain activity, eye movements, heart rate and rhythm, blood pressure, and the amount of oxygen in your blood.
This Huffington Post story compares the sleep clinic polysomnogram with four wrist based devices and a cell phone app. They did a great job of normalizing the data for a fair comparison.
Here are the results with my sleep study findings on top. Red indicates wakefulness, black is REM sleep, and blue indicates light (light blue) to deep (darker blue) sleep. I have translated the output of all of the devices into a common visual reference to allow for easier comparison. While the “look” of the data has changed, the data content has not.