Background: Monitoring the implementation of new interventions, as in this study Non-violent Resistance (NVR) for the use in residential youth care settings, is mandatory in order to evaluate, adjust and refine the implementation process where necessary. Objective: As there is no instrument for such monitoring of NVR available, the authors developed a new questionnaire, named "Reaction to Unacceptable Behavior Inventory", (in short: RUBI). Method: This questionnaire was completed by staff of four different residential settings in the Netherlands, at different stages of the NVR implementation process. The staff members reported on the practice of their colleagues. Results: The results are promising, as they show good reliability, inter-item correlations and other psychometric features for the included items. Furthermore, the results show that the RUBI seems to discriminate between trained and untrained teams, defending its use in future implementation processes and implementation research. Conclusions: The RUBI is the first attempt to create an instrument which can be used for monitoring change during implementation of NVR, and for evaluating the degree of difference or compatibility between NVR and existing practice before implementation. Longitudinal research is needed to strengthen the documentation of validity and reliability of the RUBI in different settings, countries, and cultures. This should also be extended to the final and follow-up stages of implementation. In the future, redundant and insensitive items should be removed and standards for interpreting scale scores should be developed.