Wireless Sensor Networks (WSNs) have been proposed for monitoring vital signs of patients at home. This scenario requires inter-cell mobility; however, WSNs are not designed to support this characteristic. In this paper we propose a cross-layer protocol to manage the handoff, called WSN-HaDaS (Handoff aware of Data Sending), which operates in the transport layer and medium access control (MAC) sub-layer based on an interaction between the layers (transport and MAC). This protocol interacts with a sending data mechanism (like TCP protocol) to notify the beginning or ending of the handoff process; therefore, the mechanism can stop or resume data sending, respectively. Therefore, WSN-HaDaS prevents packet loss during the handoff process. WSN-HaDaS comprises two main processes to manage mobility: Monitoring Handoff Trigger (MHT) and Handoff Execution Process (HEP); they are responsible for generating the handoff warning messages and executing the handoff process, respectively. Therefore, MHT delay and HEP delay are used as the key performance metrics. To evaluate the proposal, we use a physical test-bed in an indoor environment with the intention of obtaining practical results. The results demonstrate that the proposed protocol performs the handoff process with less delay than the selected reference work. They also show that WSN-HaDaS is an appropriate solution to provide inter-cell mobility in WSNs. Furthermore, we demonstrate the possibility of embedding the WSN-HaDaS in devices with limited resources using the IEEE 802.1.5.4 standard.