Apparatus for detecting 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, for sensing 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 for determining a force measurement using the joint sensor, and having a pre-established baseline value stored therein, and which is coupled 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 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 magnetic transducers comprise coils, and wherein the first subassembly comprises a first coil having a first coil axis parallel to the longitudinal axis of the insertion tube, and wherein the second subassembly comprises two or more other coils (66, 68, 70) in different, respective radial locations within a section of the probe that is spaced apart axially from the first subassembly, the processor applying current to one coil of the two or more other coils of the second subassembly and measuring a signal output by a remainder of the two or more other coils of the second subassembly, the signal output by a remainder of the two or more other coils of the second subassembly defining a pickup value, the processor comparing the pickup value to the pre-established baseline value and identifying a presence of a metal object near a distal end of the probe when the pickup value is outside of a range of the pre-established baseline 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, for sensing 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 for determining a force measurement using the joint sensor, and having a pre-established baseline value stored therein, and which is coupled 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 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 magnetic transducers comprise coils, and wherein the first subassembly comprises a first coil having a first coil axis parallel to the longitudinal axis of the insertion tube, and wherein the second subassembly comprises two or more other coils (66, 68, 70) in different, respective radial locations within a section of the probe that is spaced apart axially from the first subassembly, the processor applying current to one coil of the two or more other coils of the second subassembly and measuring a signal output by a remainder of the two or more other coils of the second subassembly, the signal output by a remainder of the two or more other coils of the second subassembly defining a pickup value, the processor comparing the pickup value to the pre-established baseline value and identifying a presence of a metal object near a distal end of the probe when the pickup value is outside of a range of the pre-established baseline value.