— In mobile sensor networks, self-deployment and relocation are two different research issues, both of which involve autonomous sensor movement. They share in most cases a common goal, that is, to improve overall network sensing coverage. Under this circumstance, some self-deployment algorithms may be applied to solving relocation problem without modification. However, considering efficiency, they will not be a good option in the scenario with high sensor failure rate. Existing sensor relocation protocols are not quite practical because they rely on strong assumptions and/or have weakness in maintaining network topology. In this paper, we propose a distributed zone-based sensor relocation protocol, ZONER, for mobile sensor networks on the basis of a restricted flooding technique, i.e., ZFlooding. Requiring zero-knowledge about sensor field, the ZONER is able to effectively discover previously-deployed redundant sensors without being concerned with obstacles or network ununiformit...