Dependable mobile ad-hoc networks are being designed to provide reliable and continuous service despite the failure of some of their components. One of the basic building blocks that has been identified for such fault tolerant systems is the failure detection service which aims at providing some information on which hosts have crashed. In this paper, we present a new implementation of a failure detection service for wireless ad-hoc and sensor systems that is based on an adaptation of a gossip-style failure detection protocol and the heartbeat failure detector. We show that our failure detector is eventually perfect-That is, it satisfies both properties: strong completeness and eventual strong accuracy. Strong completeness means that there is a time after which every faulty mobile is permanently suspected by every fault-free host. While, eventual strong accuracy refers to the fact that no host will be suspected before it crashes.