Failure in orienting towards occurring social stimuli represents one of the earliest and most basic social impairments in autism. Although, there are evidences for early signs of autism before three years of age, the available clinical tests for the diagnosis are not suitable for quantifying behavior alterations. There are no laboratory tests to confirm or disprove the diagnosis. My PhD work focuses on the design and development of a multimodalhead-mounted device for assessing children's orienting behavior towards social stimuli in their first three years of life. The aim of the work is to develop new methods and technologies for supporting early diagnosis of neurodevelopmental disorders with quantitative, objective observations. TACT (Thought in Action) European project guidelines have been followed for the designing of the device. Technological choices are emphasized with respect to un-obtrusive, ecological and multimodal requirements. Also ad-hoc calibration procedures suitable to unstructured environments have been developed and here presented. Preliminary tests carried out at a local daycare with 12-36 months old infants prove the in-field usability of the proposed technology. Considerations on the future development of the device stressed the meaningful contribution that such platform can offer to child-robot interaction research.