Despite the great interest received by the smartphones in opportunistic networks context, the requested energy toll still remains one of the prominent inhibiting factors to the real deployment of such technology. In this paper we evaluate a on-off approach devised to provide intermittent (but synchronized) WiFi communication across opportunistically connected devices while saving energy. Differently form classical duty cycle approaches that are implemented at the protocol/network level, we devise a "human time-scale" duty cycle that can be implemented as an overlay system service at the application level. The relatively large time-scale allows to simply keep a loose synchronization between terminals, without requiring any changes in the default operating system or system internals of commercial mobile phones.With reference to Android devices, we analyze the effects of varying such duty cycle in terms of the feasibility of the synchronization requirements as well as the energy gain obtained in order to find the trade-off for the different state settings. For these values, we evaluate the loss of discovered contacts using the data coming from real human mobility traces. © 2013 IEEE.