High-quality simulation tools are crucial to evaluate the energy efficiency of applications and protocols for wireless sensor networks in the most realistic way. Sensor node emulators like Avrora are well-suited for homogeneous networks but can not cope with heterogeneous networking scenarios. Wireless sensor networks have been used mostly isolated for special purposes in the past. But use cases like the so called smart environments require wireless sensor nodes to communicate and interact with other devices too. In this paper, we present OMNeTA as a solution to this problem, offering the ability to simulate highly heterogeneous networks of different device classes. Our hybrid simulation approach combines the proven hardware emulation by Avrora, radio communication simulation by \mixim and the flexibility of OMNeT++. Bridging the abstraction gap between hardware emulation and network simulation, OMNeTA may also reduce the effort required to experiment with new protocols, applications or other varying parameters, by enabling rapid-prototyping like development processes.