Low motor activity levels and prolonged episodes of uninterrupted immobility are characteristics of sleep. In clinical practice, the use of polysomnographic (PSG) recording is a standard procedure to assess sleep. However, PSG is not suitable for long-term monitoring in the home environment. This paper describes the development of a portable telemonitoring device that detects movements of a subject by conductive mats, and evaluates sleep stages via physical activity data. The device itself also serves as a Web server. Doctors and caregivers can access real-time and historical data via an IE browser or a remote application program for telemonitoring of physical activities and sleep/awake states during sleep, while the patients stay in their own homes. In our validation test with four normal subjects and four arousal subjects, this system showed a good performance in locating sleep epochs of a subject. The sensitivity of locating sleep epochs was 89.5% and the average positive prediction value was 94.8%, with a specificity of 84.3%. This device is not intended to be a diagnosis device, instead, it is to be used as a home telehealth tool for monitoring physical activity and sleep/awake states. This portable telemonitoring device provides a convenient approach to better understand and recognize a subject's sleep pattern through long-term sleep monitoring in the home environment.