In this talk I will present the recent paper by Fewster, Janssen, Loveridge, Waldron and myself: "Quantum reference frames, measurement schemes and the type of local algebras in quantum field theory." In this work we show how the mathematically rigorous notion of quantum reference frames allows us to generalize the results of  Chandrasekaran, Longo, Penington and Witten on observables in de Sitter spacetime. The main idea is to study the joint algebra associated with the system together with the reference frame in the presence of symmetries. If both the system and the reference frame are covariant under some symmetry group, the construction of the invariant joint algebra very naturally involves crossed products. Under some assumptions on thermal properties of the reference frame and the system, the resulting crossed product algebra is a von Neumann factor of type II_1 and hence admits a trace.