We present a model of synchronization in networks of autonomous agents where the topology changes due to agents motion. We introduce two timescales, one for the topological change and another one for local synchronization. If the former scale is much shorter, an approximation that averages out the effect of motion is available. Here we show, however, that the time required for synchronization achievement is larger than the prediction of the approximation in the opposite case, especially close to the continuum percolation transition point. The simulation results are confirmed by means of spectral analysis of the time-dependent Laplacian matrix. Our results show that the tradeoff between these two timescales, which have opposite effects on synchronization, should be taken into account for the design of mobile device networks. After an initial period of characterizing complex networks in terms of local and global statistical properties (e.g., Ref.[1]), attention turned to the dynamics of their interacting units [2]. A widely studied example of such behavior is synchronization of coupled oscillators arranged into complex networks. The interplay between topology and dynamics is crucial for synchronization achievement (see Ref.[3] and references therein). In most studies of such systems the network has a fixed structure, but there are also many interesting scenarios where the topology changes over time in various fields, such as power transmission system [4], consensus problem [5], mobile communication [6], and functional brain networks [7].Within the general framework of time-dependent or evolving networks, we can identify the particular case of networks whose nodes represent physical agents that move around but interact with each other only when they are close enough. Examples include the coordinated motions of robots [8], vehicles [9], and groups of animals [10], in which cooperative dynamics emerge. Especially, there are many examples where synchronization plays a crucial role: chemotaxis [11], mobile ad hoc networks [12], and wireless sensor networks [13]. Despite the importance of this topic, prior research on synchronization in time-dependent networks of populations of agents has concentrated so far on two special cases: (i) where the network topology changes fast [14][15][16][17] and (ii) where the population is dense and arranged in a ring [18]. In the former case, the fast-switching approximation (FSA), which averages out the effect of agent motion, is commonly used. However, for better understanding of synchronization of mobile agents and design of an efficient network, it is very important to clarify when and how FSA fails.In order to study this point, this Rapid Communication proposes a general framework in which agents perform random walks in a two-dimensional (2D) plane. We consider that each agent possesses a mobile wireless device whose state is characterized by a phase variable, and the phases approach one another through the interaction between agents within a certain spatial range. This model is we...