Adaptive Transmission Power Protocol for heterogeneous Wireless Sensor Networks A novel communication protocol – Adaptive Transmission Power Protocol – for Wireless Sensor Networks with the facility of reconfiguring the transmission power of the hardware is presented. Specifications of the protocol including the packet format and the contention avoidance methods are described. The protocol is implemented on a hardware platform and the performance is considered for a fundamental operation. The results show that non-overlapping regions exist for different transmission power levels where the system performance is optimum. More importantly, these regions move farther from the node with increase in transmission power level. It is observed that reconfiguring transmission power levels is an effective way of saving energy in Wireless Sensor Networks, the operation of which is abstracted by the implementation of the Adaptive Transmission Power Protocol.