  In this study, Call Detail Records (CDR), covering Budapest, Hungary has been
processed to analyze the circadian rhythm of the subscribers. An indicator,
called wake-up time, is introduced to describe a behavior of a group of
subscribers. It is defined as the time, when the mobile phone activity of a
group rises in the morning. Its counterpart is the time, when the activity
falls in the evening. Inhabitant and area-based aggregation are also presented.
The former is to consider the people who live in an area, the latter uses the
transit activity in an area to describe the behavior of a part of the city. The
opening hours of the malls and the nightlife of the party district was used to
demonstrate this application, as real-life examples. The proposed approach was
also used to estimate the working hours of the workplaces. The findings are in
a good agreement with practice in Hungary, and also support the workplace
detection method. Negative correlation was found between wake-up time and
mobility indicators (Entropy, Radius of Gyration): On workdays, people wake up
earlier and travel more, on holidays it is quite the contrary. The wake-up time
was evaluated in different socioeconomic classes, using housing prices and
mobile phones prices, as well. It was found that lower socioeconomic groups
tend to wake up earlier.
