Apparatus configured to detect metal disturbance during a medical procedure comprising: a probe, which comprises: an insertion tube, having a longitudinal axis and having a distal end; a distal tip, which is disposed at the distal end of the insertion tube and is configured to be brought into contact with tissue of the body; a joint, which couples the distal tip to the distal end of the insertion tube; and a joint sensor, contained within the probe, configured to sense a position of the distal tip relative to the distal end of the insertion tube, the joint sensor comprising a first subassembly and a second subassembly, which are disposed within the probe on opposite, respective sides of the joint and each comprise one or more magnetic transducers (64, 66, 68, 70); and characterized by: a processor configured to determine a force measurement using the joint sensor, and having a threshold field value stored therein, and which is coupled and configured to apply a current to one of the first subassembly and the second subassembly, thereby causing the one of the first subassembly and the second subassembly to generate at least one magnetic field, and which is coupled to receive and configured to process one or more signals output by the other of the first subassembly and the second subassembly responsively to the at least one magnetic field so as to detect changes in a position of the distal tip relative to the distal end of the insertion tube, wherein the one or more signals output by the other of the first subassembly and the second subassembly define a sensed field value, the processor configured to compare the sensed field value to the threshold field value and to identify a presence of a metal object near a distal end of the probe when the sensed field value is below the threshold field value. a probe, which comprises: an insertion tube, having a longitudinal axis and having a distal end; a distal tip, which is disposed at the distal end of the insertion tube and is configured to be brought into contact with tissue of the body; a joint, which couples the distal tip to the distal end of the insertion tube; and a joint sensor, contained within the probe, configured to sense a position of the distal tip relative to the distal end of the insertion tube, the joint sensor comprising a first subassembly and a second subassembly, which are disposed within the probe on opposite, respective sides of the joint and each comprise one or more magnetic transducers (64, 66, 68, 70); and characterized by: a processor configured to determine a force measurement using the joint sensor, and having a threshold field value stored therein, and which is coupled and configured to apply a current to one of the first subassembly and the second subassembly, thereby causing the one of the first subassembly and the second subassembly to generate at least one magnetic field, and which is coupled to receive and configured to process one or more signals output by the other of the first subassembly and the second subassembly responsively to the at least one magnetic field so as to detect changes in a position of the distal tip relative to the distal end of the insertion tube, wherein the one or more signals output by the other of the first subassembly and the second subassembly define a sensed field value, the processor configured to compare the sensed field value to the threshold field value and to identify a presence of a metal object near a distal end of the probe when the sensed field value is below the threshold field value. a processor configured to determine a force measurement using the joint sensor, and having a threshold field value stored therein, and which is coupled and configured to apply a current to one of the first subassembly and the second subassembly, thereby causing the one of the first subassembly and the second subassembly to generate at least one magnetic field, and which is coupled to receive and configured to process one or more signals output by the other of the first subassembly and the second subassembly responsively to the at least one magnetic field so as to detect changes in a position of the distal tip relative to the distal end of the insertion tube, wherein the one or more signals output by the other of the first subassembly and the second subassembly define a sensed field value, the processor configured to compare the sensed field value to the threshold field value and to identify a presence of a metal object near a distal end of the probe when the sensed field value is below the threshold field value.