A wetness sensor, comprising: a first substrate (414, 514); and a tuned RF circuit (416, 516) carried by the first substrate, the RF circuit including a first conductive pattern, a first separate capacitor (420, 520), and a separate jumper (424, 524) all disposed on a same side of the first substrate, the RF circuit being characterized by an impedance or resistance; wherein the first conductive pattern includes a coil (418, 518), an inner terminus (423a, 523a) on an interior of the coil (418, 518), and an outer terminus (423b, 523b) on an exterior of the coil (418, 518); wherein the jumper (424, 524) is formed from a conductive material to electrically couple the inner terminus (423a, 523a) to the outer terminus (423b, 523b), wherein said jumper is configured to avoid making electrical contact with the portions of the conductive pattern that it crosses over; and wherein the jumper (424, 524) includes a frangible link that comprises either a non-conductive adhesive that connects the jumper or a portion thereof to the sensor substrate, the adhesive being adapted to dissolve when contacted by the target, or alternatively or in addition, a second substrate that forms part of the jumper, the second substrate being adapted to dissolve, swell or degrade when contacted by a target fluid such that the impedance or resistance of the RF circuit changes by at least a factor of 5 when the frangible link is contacted by the target fluid. a first substrate (414, 514); and a tuned RF circuit (416, 516) carried by the first substrate, the RF circuit including a first conductive pattern, a first separate capacitor (420, 520), and a separate jumper (424, 524) all disposed on a same side of the first substrate, the RF circuit being characterized by an impedance or resistance; wherein the first conductive pattern includes a coil (418, 518), an inner terminus (423a, 523a) on an interior of the coil (418, 518), and an outer terminus (423b, 523b) on an exterior of the coil (418, 518); wherein the jumper (424, 524) is formed from a conductive material to electrically couple the inner terminus (423a, 523a) to the outer terminus (423b, 523b), wherein said jumper is configured to avoid making electrical contact with the portions of the conductive pattern that it crosses over; and wherein the jumper (424, 524) includes a frangible link that comprises either a non-conductive adhesive that connects the jumper or a portion thereof to the sensor substrate, the adhesive being adapted to dissolve when contacted by the target, or alternatively or in addition, a second substrate that forms part of the jumper, the second substrate being adapted to dissolve, swell or degrade when contacted by a target fluid such that the impedance or resistance of the RF circuit changes by at least a factor of 5 when the frangible link is contacted by the target fluid. either a non-conductive adhesive that connects the jumper or a portion thereof to the sensor substrate, the adhesive being adapted to dissolve when contacted by the target, or alternatively or in addition, a second substrate that forms part of the jumper, the second substrate being adapted to dissolve, swell or degrade when contacted by a target fluid such that the impedance or resistance of the RF circuit changes by at least a factor of 5 when the frangible link is contacted by the target fluid.