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We study the problem of waking up a collection of n processors connected by a multihop ad hoc ratio network with unknown topology, no access to a global clock, and no collision detection mechanism available. Each node in the network either wakes up spontaneously or gets activated by receiving a wake‐up signal from another node. All active nodes transmit the wake‐up signals according to a given protocol $\calW$. The running time of $\calW$ is the number of steps counted from the first spontaneous wake‐up until all nodes become activated. We provide two protocols for this problem. The first one is a deterministic protocol with running time . Our protocol is based on a novel concept of a shift‐tolerant selector to which we refer as a (radio) synchronizer. The second protocol is randomized, and its expected running time is , where D is the diameter of the network. Subsequently we show how …