This paper presents a distributed algorithm for efficient Time Division Multiple Access (TDMA) slot allocation in Wireless Sensor Networks. Unlike most of the existent proposals, which try to guarantee interference-free allocation based on the n-hop criterion (which can only work with regular topologies), the presented algorithm bases its decisions on the received signal strength, allowing it to operate independently of the WSN topology. The performance of the proposed slot allocation algorithm was compared with centralized depth-first slot allocation using computer simulation. The results show that the proposed scheme is significantly faster, only paying the price of extra energy consumption during the initial network setup phase.