Wireless Sensor Networks promise a new instrument for monitoring and collecting data about some outside world phenomenon. Since sensor nodes would embed valuable information, the failure of these nodes would cause the false alarms or missed detections. One solution is to use space-redundant technique along with the incremental checkpointing to save the sensor nodes states. Nevertheless, previous incremental checkpoint relies on the page protection hardware. Since sensor nodes do not have the page protection hardware, previous incremental checkpointing cannot be applied. In this paper, we thus propose three incremental checkpoint methods in MMU-less sensor networks. These three methods differ in the granularity of checkpoint unit and the module execution overhead. We have implemented the three incremental checkpointings on SOS in the mica2 mote sensor nodes. According to the experimental results, we checkpoint and restore the application state successfully. Besides, depending on the characteristics of a module, each application modules can select its own incremental checkpoint scheme to minimize the checkpoint overhead.