We are presenting a novel approach for very low cost 3D inertial sensor. The idea consists in using on same device MEMS and NEMS technologies. The MEMS part is used for the mass to keep sufficient inertial force, and the NEMS is used as a very sensitive sub-μm suspended stress gauge. This way enables the detection of in-plane and out-of-plane acceleration on a same device and with differential detection means (to reduce thermal sensitivity). Technological realization and first characterizations of the accelerometer have been achieved and are detailed in this paper. Accelerometer area is around 0.1mm2 per axis, which means at least 3 to 5 times smaller than conventional MEMS accelerometers. Moreover, the performances are compatible with typical consumer market accelerometer specifications.