The diagnosis of sleep disorders, highly prevalent in Western countries, typically involves sophisticated procedures and equipment that are highly intrusive to the patient. The high processing capabilities and storage capacity of current portable devices, together with a big range of available sensors, many of them with wireless capabilities, create new opportunities and change the paradigms in sleep studies. In this work, a smartphone based sleep monitoring system is presented along with the details of the hardware, software and algorithm implementation. The aim of this system is to provide a way for subjects, with no pre-diagnosed sleep disorders, to monitor their sleep habits, and on the initial screening of abnormal sleep patterns.