Sensor nodes are heavily constrained regarding energy resources. The development of energy efficient application and protocols is therefore one of the most important issues in Wireless Sensor Networks (WSNs). However, most publications up to now avoid the complexity of realistic energy evaluations and oversimplify their evaluation at this point. This work aims at lowering the barrier for realistic energy evaluations by pointing out the most important challenges and pitfalls. For a realistic and distributed evaluation of energy consumption, the WSN Testbed for Network Management and Energy Monitoring (SANDbed) is used. We present evaluation results of a simple example application that just transmits one single packet using TinyOS Low Power Listening (LPL). Although being a simple example, packet transmission is part of almost any WSN application. The shown results are therefore important to many WSN protocol evaluations.