Abstract: The IEEE 802.15.4 specification is a recent low data rate wirelesspersonal area network standard. While basic security services areprovided for, there is a lack of more advanced techniques which areindispensable in modern personal area network applications. In addition,performance implications of those services are not known. In this paper,we describe a secure data exchange protocol based on the ZigBeespecification and built on top of IEEE 802.15.4 link layer. Thisprotocol includes a key exchange mechanism. We assume that all nodes areapplying power management technique based on the constant event sensingreliability required by the coordinator. Power management generatesrandom sleep times by every node which in average fairly distributes thesensing load among the nodes. Key exchange is initiated by a clustercoordinator after some given number of sensing packets have beenreceived by the coordinator. We develop and integrate simulation modelof the key exchange and power management technique into the cluster's reliablesensing function. We evaluate the impact of security function and itsperiodicity on cluster performance.