There are context-dependent behaviors that are active only when a certain condition holds, and that require a certain transition process before activation. We propose a layer-activation mecha- nism of context-oriented programming languages for such context- dependent behaviors. Our mechanism supports the implicit layer activation (as opposed to the event-based layer activation) in a sense that a condition of activation is written as a conditional ex- pression over reactive values (e.g., values obtained from sensors). In addition, it is push-based in a sense that it executes the tran- sition process immediately after the condition becomes valid (as opposed to the mechanisms that defer the transition process until the first execution of a context-dependent behavior). In this paper, we present how this mechanism works in an extension of ServalCJ with push-based reactive values, and identify open issues raised by this proposal.