We report a continuousmeasurement of the spin state of a spinor BEC. A far off-resonant linearly polarised probe beam illuminates a sodium spinor condensate in F=1. The beam is Faraday rotated in proportion to the spin component along the beam propagation direction, and the rotation measured at the shot-noise limit with an autobalanced polarimeter. The measurement is minimallydestructive and continuous. As the condensate spin Larmor precesses in a weak magnetic bias field, the Faraday signal oscillates at the Larmor frequency, typically of order 50 kHz. We investigate this novel measurement for monitoring spin-mixing and decoherence processes in real time.