According to the manufacturer's instructions, the BSA was placed over the triceps muscle of the right arm, at the midpoint between the acromion and olecranon processes of all participants during PSG monitoring. The BSA is a portable sensing device, 8.8 × 5.6 × 2.1 cm in size and 82 g in weight that can provide information regarding the total energy expenditure, TST, and circadian rhythm.[15 (link)] The sensors in the BSA measure skin temperature, galvanic skin response, heat flux from the body, and movement. These physiological data are then processed by advanced algorithms to calculate and report total energy expenditure, metabolic physical activity, and sleep duration in free-living environment.[15 (link)16 ] However, in this study, we analyzed data related to accelerometry (movement) only to validate the detection of sleep and wake in patients with OSA using BSA. The BSA accelerometer is similar to wrist actimeter (actigraphy), except for the fact that BSA is worn over the arm and it utilizes a dual axis accelerometer. The accelerometer uses a micro-electro-mechanical sensor (MEMS) device that detects and measures motion. The built-in accelerometer has a scale of ±2 g and a sensitivity of 167 mV/g. Data about sleep for both BSA and PSG were classified in a binary form into wake = 0 and sleep (any stage) = 1. The BSA is limited to estimating wake and sleep in 1 minute epochs. The computers recording the data of the PSG and BSA were synchronized to a standard time and the data analysis window for the BSA was marked to match the lights out and lights on from PSG. The sensor was monitored 32 times per second, and data tracked over a period of 1 minute.[17 ] Minute-by-minute data from the BSA were analyzed by algorithms using Body Media® InnerView® Research Software (version 5.1) provided by BodyMedia, Inc.[16 ]