Abstract: Hybrid MAC protocol design in wireless sensor networks becomes vibrant research field for the past several years. The ubiquitous plug and play characteristics of commercially available open source hardware paved way for the development of smart wireless sensor network. Wireless sensor networks can be termed as a new generation of distributed embedded systems that has a capability of meeting broad range of real-time applications. Examples includehome automation, industrial automation, power plant monitoring, radiation monitoring, fire monitoring, pipeline monitoring and control, border surveillance, medical care etc. Wireless sensor networks that are deployed in time critical or mission-critical applications with highlydynamic environments have to interact with the physical phenomenon under stringent timingconstraints and severe resource limitations. The proposed hybrid ET-MAC (Emergency Threshold MAC) protocol targets advanced home automation which require careful MAC protocol design for safety critical low latency, reliability and end to end delay as a primary concernand secondary concern can be given for parameters like residual energy, energy efficiency etc. Supportingreal-time QoS faces severe challenges due to the wireless nature, limited resource, low node reliability, distributedarchitecture and dynamicnetwork topology.This paper presents the design, implementation and performance evaluation of a hybrid ET-MAC protocol with prioritization of nodeswhich adopts a TDMA approach to schedule collision-free slots during emergency periodand CSMA/CA approach during normal operation conditions in time/mission critical applications to avoid collision andto have low latency. The proposed MAC protocol is simulated in NS2 environment and from the results, it is observed that proposed protocol performs better than conventional MAC protocols in terms of energy efficiency and offering low latency.