A wearable device includes a main body, and a strap connected to the main body, the strap being configured to be flexible. The wearable device further includes a light source disposed in the strap, the light source being configured to emit light onto a surface of a user. The wearable device further includes a spectrum portion disposed in the main body, and an optical waveguide disposed in the strap, the optical waveguide being configured to receive the emitted light traveling into and out from the surface, and transmit the received light to the spectrum portion. The wearable device further includes a detector disposed in the main body, the detector being configured to detect the transmitted light dispersing through the spectrum portion.
