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In order to diagnose sleep apnea-hypopnoea syndrome (SAHS) automatically without using contact-type sensors, we developed a non-contact screening method using amplitude probability (AP) of a compact microwave radar output amplitude which corresponds to respiratory chest movements. We conducted non-contact respiration monitoring of elderly subjects in bed using dual 24-GHz microwave radars attached beneath mattress of a bed. The respiration amplitudes of SAHS patients fluctuate while asleep. AP means a probability of respiration amplitudes falling below a threshold level (%RMS of radar output amplitude). In order to assess the efficacy of this screening method, we tested on 14 elderly non-SAHS subjects and four elderly SAHS subjects (88.0 ± 9.9 years) at a nursing home. The proposed method achieved 100% sensitivity when we set AP and %RMS, 0.3 and 50, respectively.