Directional antennas in sensor networks are receiving increasing interest and research due to the potential to increase throughput and reduce delay and interference, while requiring lower transmission power. Considering the stringent operation requirements (low duty-cycle) as MAC congestion problems in large multi-hop networks, WSN performance can benefit enormously from such directional capabilities together with an intelligent design. This paper investigates the introduction of switched beam directional antennas in sensor networks using a synchronised sleep/awake contention-base MAC (DirC-MAC) and real available hardware solutions. The control simplicity, small size and low cost makes switched beam antenna technology an attractive and suitable solution for sensor nodes. By means of modelling off-the-shelf sensor node architecture and the use of network simulation this paper shows significant improvements (up to 4 times more throughput and half battery used) may be achieved using directional antennas compared to the omnidirectional alternative. This paper emphasises the use of more realistic radio channel assumptions and addresses the impact of directional antennas in contention-based MACs analysing the performance of different handshaking mechanisms.