In this paper we study how to detect anomalies in a distributed manner by using wireless sensor networks (WSN). We focus on a medical context, where existing works generally provide large environments to monitor patients using sensors as simple transducers. Those devices forward sensed health parameters to a main base station. This station collects received data and may perform some computations. In this paper, we perform some distributed tasks on the sensors. We propose a distributed algorithm which allows to raise alarms under some initial rules to alert efficiently medical staff in case of critical situations without needles warnings.