Actigraphy is a non-invasive method of monitoring human rest/activity cycles.
It is like a "medical grade" activity monitor used for athletics. The unit is usually, in a wrist-watch-like package, worn on the wrist.
The movements the actigraph unit undergoes are continually recorded and some units also measure light exposure.< p>The data can be later read to a computer and analyzed offline; in some brands of sensors the data is transmitted and analyzed in real time.
A sleep diary is used with the actigraph to undestand your sleep wake cycles.