You need to readout your personal dosimeter at least once per month at one of the reader stations installed at a large number of locations around CERN. Regular readout is essential to ensure the periodic monitoring of your personal dose. The monthly readout is also required by the Swiss and French Authorities. When you leave CERN for a longer period than a month, you have to return your dosimeter to the Dosimetry Service - once you come back to CERN you can go and pick up your dosimeter at the dosimetry service for the time you need it, as long as your RP course and medical certificate are valid.
In order to facilitate the attribution of a dosimeter while coming back at Cern, please send an email to the dosimetry.service@cern.ch, copy to the secretariat, few days before coming as they can prepare it. In case you are coming during the week-end, a colleague or the secretariat can collect it days before.
For more information: https://dosimetry.web.cern.ch/en/dosimeter