IEEE 802.15.4 protocol has attracted much attention in research and industrial communities as candidate technology for wireless body area sensor networks (WBASNs). IEEE 802.15.4 supports the exclusive use of a wireless channel through guaranteed time slot (GTS). However, on one hand, bandwidth underutilization rate may be lower because of the variance between the guaranteed bandwidth and the arrival rate. On the other hand, the waiting time for transmitting emergency notification is getting longer when the GTSs assigned to the nodes increase in WBASNs. To solve these problems, in this article, a new scheme is proposed to reduce transmission delay for the alarm notification in emergent situations. Simulation results are presented to validate the efficiency of the proposed scheme by comparing it with the medium access control (MAC) protocol of IEEE 802.15.4.