The invention discloses a wearable physiological activity sensor, a sensing device and a sensing system. In an implementation example, the wearable physiological activity sensor comprises an intra-ear housing on which an electrode for encephalograms is installed, wherein the size and the shape of the intra-ear housing are constructed to be connected with at least part of the cavum conchae, cymba conchae, and/or intertragic notch of an auricle of a user, and further constructed to provide a stable jacking force for jacking the cavum conchae, the antitragus, the tragus and/or the intertragic notch of the auricle at the position of the electrode for encephalograms, so that a brain electric signal is conveniently obtained by the electrode for encephalograms.
Wearable physiological activity sensor, sensing device and sensing system