In this study, we propose an efficient wearable device to continuously and reliably monitor electrocardiogram (ECG) and body impedance (BI) that are two most important bio-signals for healthcare applications. Unlike most conventional systems that fail to synchronously provide a rich set of bio-signals because of their limitation on sensing a single type of signal, the proposed device faithfully analyzes a user's status only using two electrodes. To minimize measurement errors inherently induced by the sensing process caused by using two electrodes and sensing position dependency, we also propose an adaptive system control algorithm that are easy to switch the type of sensing signal and its measurement intervals by changing the setup parameters. Since the size of the device is very small and it is designed with a minimal belt-shape form for maximal user convenience, it is suitable for various types of wearable applications. Experiments performed in a couple of example healthcare scenario demonstrate the reliability of the proposed system.