Our work intends to verify reactive systems with event memorization specified with the reactive language Electre. For this, we define a particular behavioral model for Electre programs, Reactive Fiffo Automata (RFAs), which is close to Fifo Automata. Intuitively, a RFA is the model of a reactive system which may store event occurrences that must not be immediately taken into account. We show that, contrarily to lossy systems where the reachability set is recognizable but not effectively computable, (1) the reachability set of a RFA is recognizable, and (2) it is effectively computable. Moreover, we also study the relationships between RFAs and Finite Automata and we prove that (3) from a trace language point of view, inclusions between RFAs and Finite Automata are undecidable and (4) the linear temporal logic LTL on states without the temporal operator next is decidable for RFAs, while LTL on transitions is undecidable.