A occlusion detector for a dual-port surgical tourniquet system comprises: a tourniquet cuff for encircling a patient's limb and including an inflatable portion that communicates pneumatically with a first cuff port and that communicates pneumatically with a second cuff port independently of the first cuff port; a tourniquet instrument that is releasably connectable to the first and second cuff ports to establish first and second pneumatic passageways between the tourniquet cuff and the tourniquet instrument, wherein the tourniquet instrument includes pressure sensing means communicating with the first pneumatic passageway for producing an indication of the pressure in the cuff over a time period suitably long for the performance of a surgical procedure, pressure regulation means communicating with the second pneumatic passageway for regulating the pressure in the cuff near a reference pressure level, and an occlusion detector for introducing a pneumatic pressure pulse into the first pneumatic passageway during an occlusion detection time period, for monitoring the pressure in the second pneumatic passageway during the occlusion detection time period, and for producing an occlusion alarm if a fluctuation of pressure in the second pneumatic passageway is not detected within the occlusion detection time period.