Activity trackers are used in a wide range of research, from movement science to psychiatry, from criminology to rehabilitation science. In this talk, we will outline the requirements for activity trackers to be used as research devices. Legal and design aspects will be highlighted as well as the view from data science and field research. We will show how an open source alternative to the currently used devices is a ( is the only?) way forward. Activity trackers, such as fitbits are widely used amongst researchers to collect physiological and behavioral data in lab settings as well as in natural settings. In this talk, we will focus on data collection in natural settings and first outline the requirements a research device has to fulfill. More specifically, we will highlight the data privacy and protection aspects, as well as aspects of data collection that allows not only social scientists to use the data but also data scientists to learn from the collected data. In the second half of the talk, we will first present the platform we developed to collect data with a Samsung customer grade fitness tracker and then suggest an open source and open hardware solution to overcome the obstacles that researchers currently face. The first design decisions to create a community lead platform are presented and the design process highlighted. In the last part of the talk, the audience is invited to contribute with feedback in a structured manner, to make the next steps towards a modular and open Fitnesstracker for research purposes. The work on the Samsung platform is done in cooperation with Peter Bosch, Lieuwe Rooijakkers and Frederick van der Meulen (all CS students at Leiden University). The work on the process design has been done together with Assia Kraan (Hogeschool Amsterdam), Ricarda Proppert (Leiden University) and Klodiana-Daphne Tona (Leiden University and Medical Center).