As the services of Wireless Sensor Networks (WSNs), M2M and IoT are becoming more varied, reliable data transmission should basically be assured to support the required QoS specifications of sophisticated services in WSNs. However, the probability of collision is increased due to the crowded wireless frequency, WSNs have strict constraints on resources; therefore a more efficient way of delivering the data is required in terms of delay time and energy consumption. This paper proposes an improved and reliable data transmission ARQ method called E2R-ACK (Energy Efficient and Reliable ACK), which is more efficient compared to legacy ARQ schemes such as ACK, NACK and I-ACK, as ACK consumes too much energy, NACK requires a longer delay time, and I-ACK has the drawback of the duplicate retransmission problem. The proposed E2R-ACK can improve the performance in terms of delay time and energy consumption at the same time. The methods of analyzing RcR (Resource considered Reliability), delay time and energy consumption are also presented. The results of the analysis and simulation are compared with the legacy methods. As a result of the simulations, E2R-ACK shows the better performance than legacy schemes