This paper presents an adaptive energy-efficient MAC protocol for wireless sensor networks (WSNs), called Adaptive SMAC (A-SMAC), which improves upon the original S-MAC protocol. The primary goal is to maximize the network lifetime by reducing energy consumption and latency. A-SMAC introduces coordinated sleeping among neighboring nodes to reduce control overhead and enable traffic-adaptive wake-up. It is a contention-based protocol based on the CSMA/CA mechanism. The protocol is simulated in NS-2 and evaluated under various topologies and traffic conditions. Additionally, the paper introduces a new design called Adaptive Cross MAC (ACROSS) to further improve energy efficiency by leveraging cross-layer design principles. ACROSS utilizes routing information at the network layer to maximize the sleep duration of each node. It categorizes nodes into three types based on their state in data transmission: Communicating Parties, Upcoming Communicating Parties, and Third Parties. The protocol minimizes energy consumption by turning off the radio interface of unnecessary nodes not included in the routing path. The results show that A-SMAC achieves satisfactory performance under both low and high traffic conditions, although it has issues with energy efficiency. ACROSS is proposed to address these issues by improving energy efficiency through cross-layer design. The simulation results demonstrate that A-SMAC and ACROSS outperform traditional MAC protocols in terms of energy consumption and latency. The paper also evaluates the performance of A-SMAC in different network topologies, including two-hop networks, linear multi-hop networks, and dense multi-hop networks with 25 nodes. The results show that A-SMAC achieves significant energy savings in low traffic situations and performs well under high traffic conditions. The paper concludes that A-SMAC is a promising MAC protocol for WSNs, and ACROSS is a potential improvement for further enhancing energy efficiency.This paper presents an adaptive energy-efficient MAC protocol for wireless sensor networks (WSNs), called Adaptive SMAC (A-SMAC), which improves upon the original S-MAC protocol. The primary goal is to maximize the network lifetime by reducing energy consumption and latency. A-SMAC introduces coordinated sleeping among neighboring nodes to reduce control overhead and enable traffic-adaptive wake-up. It is a contention-based protocol based on the CSMA/CA mechanism. The protocol is simulated in NS-2 and evaluated under various topologies and traffic conditions. Additionally, the paper introduces a new design called Adaptive Cross MAC (ACROSS) to further improve energy efficiency by leveraging cross-layer design principles. ACROSS utilizes routing information at the network layer to maximize the sleep duration of each node. It categorizes nodes into three types based on their state in data transmission: Communicating Parties, Upcoming Communicating Parties, and Third Parties. The protocol minimizes energy consumption by turning off the radio interface of unnecessary nodes not included in the routing path. The results show that A-SMAC achieves satisfactory performance under both low and high traffic conditions, although it has issues with energy efficiency. ACROSS is proposed to address these issues by improving energy efficiency through cross-layer design. The simulation results demonstrate that A-SMAC and ACROSS outperform traditional MAC protocols in terms of energy consumption and latency. The paper also evaluates the performance of A-SMAC in different network topologies, including two-hop networks, linear multi-hop networks, and dense multi-hop networks with 25 nodes. The results show that A-SMAC achieves significant energy savings in low traffic situations and performs well under high traffic conditions. The paper concludes that A-SMAC is a promising MAC protocol for WSNs, and ACROSS is a potential improvement for further enhancing energy efficiency.