In an aging population, technology-based solutions such as Ambient Assisted Living (AAL) systems are indispensable for supporting senior citizens in retaining their independence. Senior citizens have different physical abilities, contexts of use, and attitudes towards technology than younger user groups. This calls for a different approach to assure their acceptance of technologies. In the STuDi research project, we constructed a set of interview guidelines based on literature on technology acceptance and requirements elicitation and validation with senior citizens, and conducted 33 validation interviews with senior citizens who used a prototypical AAL system for 5–12 months. The guidelines facilitated pleasant conversations and helped obtain a good understanding of factors contributing to acceptance versus avoidance and dismissal of the AAL system. We share the findings of our literature search and the resulting interview guidelines, which we consider a suitable instrument for researchers and practitioners for measuring technology acceptance and/or validating a (prototypical) system with senior citizens, and possibly also for requirements elicitation.