In this paper, a fully-enclosed wrist-wearable hybrid nanogenerator (WHN) based on electromagnetic-triboelectric mechanism is reported with an outstanding energy harvesting performance. The proposed WHN integrates rolling electromagnetic induction and electrostatic induction of a free-standing spherical magnetic inside a hollow circular tube. The human wrist motion initiates the magnetic ball to freely roll inside the tube, generating both electromagnetic and triboelectric energy. The WHN is capable of converting diverse human wrist biomechanical energy such swinging, waving, shaking, etc. into a useful electrical energy which can continuously power the wrist-wearable electronic devices and sensors such as wrist-watch, fitness band and so on. The experimental results show that the WHN can deliver the average power of 3.46 mW under the load resistance of 100 Ω. A commercial electronic wrist-watch is successfully powered continuously for more than 18 mins from just 5 s of wrist motion by wearing WHN on wrist. Also, a commercial temperature sensor is driven for 132 s form 88 s of slow walking by wearing WHN on wrist. Remarkably, the experimental results and outstanding demonstration shows the wide potential of the WHN as a sustainable power supply for developing self-powered wearable healthcare monitoring sensors.