How are nuclear submarines tracked?

Usually the country that owns the sub can't even track it, because they are so quiet, but a lucky sonar operator might pick it up. Actual methods are classified and highly sensitive. Satellites look for heat signatures and sonar systems listen for machinery. SOSUS networks have been laid on the ocean floor at strategic locations to monitor the departure and arrival of submarines into and out of enemy ports. However once the submarines travel beyond the monitoring points, the submarine's location is, as has been mentioned, the results of a proficient sonor operation.