Recently, a noninvasive medical device (SD-101) capable of detecting breathing pattern changes in a subject lying supine or on the side has been developed. We therefore tested whether the SD-101 would be useful for diagnosing sleep apnea syndrome (SAS). Seventy patients who had been suspicious of SAS were enrolled (M/F = 61/9, mean age +/- SD = 46.6 +/- 14.7 y/o). They took 2 distinct screening tests for SAS (using the SD-101 and one of the most popular screeners for SAS in Japan (Apnomonitor III: AP, Chest Co., Tokyo)) and a simultaneously performed standard polysomnography (PSG). All patients were then asked to respond to a questionnaire on awareness of invasiveness experienced during each study (both from the screeners and from the standard PSG). The data were then compared with those from PSG mainly using correlation coefficients and the x2 test for analysis of subjective invasiveness. Statistical significance was defined as a p value of less than 0.05. As a result, the apnea-hypopnea index (AHI) from SD-101 (r=0.947, p<0.0001) had a significantly higher correlation coefficient (p<0.0001) than that from the AP (r=0.601, p<0.0001) in relation to that from PSG. The SD-101 had a significantly lower invasiveness than either AP or PSG (p<0.0001). In conclusion, SD-101 could be much more useful for checking AHI than other conventional screeners, such as AP, which suggests that SD-101 is more useful for defining SAS.