Next generation mobile ad-hoc applications will revolve around users' need for sharing content/presence information
with co-located devices. However, keeping such information fresh requires frequent meta-data exchanges,
which could result in significant energy overheads. To address this issue, we propose distributed algorithms
for energy efficient dissemination of presence and content usage information between nodes in mobile ad-hoc
networks. First, we introduce a content dissemination protocol (called CPMP) for effectively distributing frequent
small meta-data updates between co-located devices using multicast. We then develop two distributed
algorithms that use the CPMP protocol to achieve "phase locked" wake up cycles for all the participating nodes
in the network. The first algorithm is designed for fully-connected networks and then extended in the second to
handle hidden terminals. The "phase locked" schedules are then exploited to adaptively transition the network
interface to a deep sleep state for energy savings. We have implemented a prototype system (called "Where-Fi")
on several Motorola Linux-based cell phone models. Our experimental results show that for all network topologies
our algorithms were able to achieve "phase locking" between nodes even in the presence of hidden terminals.
Moreover, we achieved battery lifetime extensions of as much as 28% for fully connected networks and about
20% for partially connected networks.