Abstract: Verification apparatus (32), for verifying the location of an object (22) in a patient's body (20), the apparatus having learn and test modes and including a receiver (76), which receives signals from the object responsive to the location thereof. A parameter vector is derived from the signals. A memory (58) records a learn value of the parameter vector in the learn mode. A processor (54) receives a test value of the parameter vector in the test mode, and determines whether the test value is within a predetermined range of the learn values so as to verify the location of the object (22).