A wireless sensor network is always an integrated part of a system. The physical and logical structure of the system, where the sensor network is integrated, are together with other environmental requirements the constraints for the design of the network and the wireless sensor devices. These requirements are very different for different applications and even for one specific system the requirements may be very different on the sensor devices. When developing efficient wireless sensor devices these constraints must be taken into consideration. The diverse constraints we are facing when developing wireless sensor networks and devices for various applications makes it necessary to have a platform-based development approach where as much of the components can be re-used. For the communication, the standard IEEE 802.15.4 provides an excellent platform for developing short range power aware sensor networks. In this paper a hardware platform is presented with its modular structure it provides a highly flexible solution suitable for rapid prototyping of wireless sensors. This platform is a tool for developers of wireless sensor devices as well as system integrators that need to explore different system solutions experimentally