A body-mountable device (110, 210, 310) comprising: a polymeric material (120, 220); characterized in that the body-mountable device (110, 210, 310) further comprises: a substrate (130, 230) at least partially embedded within the polymeric material (120, 220); an antenna (170, 270, 312) disposed on the substrate (130, 230); a conductivity sensor (163, 260, 320) disposed on the substrate (130, 230), wherein the conductivity sensor (163, 260, 320) includes: a frame (263, 265, 304, 305) having a trench formed therein that defines a fluid sample cell (262, 324), wherein the trench includes a first sidewall and a second sidewall, a first electrode (264, 322) formed on the first sidewall, and a second electrode (266, 323) formed on the second sidewall such that the first and second electrodes are on opposite sides of the fluid sample cell (262, 324); and a controller (150, 250) electrically connected to the sensor electrodes (264, 266, 322, 323) and the antenna (170, 270, 312), wherein the controller (150, 250) is configured to: (i) apply a voltage to the electrodes (264, 266, 322, 323) sufficient to generate a current through the electrodes (264, 266, 322, 323) related to a conductance of a fluid occupying the fluid sample cell (262, 324); (ii) measure the generated current; and (iii) use the antenna (170, 270, 312) to indicate the measured current. a polymeric material (120, 220); characterized in that the body-mountable device (110, 210, 310) further comprises: a substrate (130, 230) at least partially embedded within the polymeric material (120, 220); an antenna (170, 270, 312) disposed on the substrate (130, 230); a conductivity sensor (163, 260, 320) disposed on the substrate (130, 230), wherein the conductivity sensor (163, 260, 320) includes: a frame (263, 265, 304, 305) having a trench formed therein that defines a fluid sample cell (262, 324), wherein the trench includes a first sidewall and a second sidewall, a first electrode (264, 322) formed on the first sidewall, and a second electrode (266, 323) formed on the second sidewall such that the first and second electrodes are on opposite sides of the fluid sample cell (262, 324); and a controller (150, 250) electrically connected to the sensor electrodes (264, 266, 322, 323) and the antenna (170, 270, 312), wherein the controller (150, 250) is configured to: (i) apply a voltage to the electrodes (264, 266, 322, 323) sufficient to generate a current through the electrodes (264, 266, 322, 323) related to a conductance of a fluid occupying the fluid sample cell (262, 324); (ii) measure the generated current; and (iii) use the antenna (170, 270, 312) to indicate the measured current. a substrate (130, 230) at least partially embedded within the polymeric material (120, 220); an antenna (170, 270, 312) disposed on the substrate (130, 230); a conductivity sensor (163, 260, 320) disposed on the substrate (130, 230), wherein the conductivity sensor (163, 260, 320) includes: a frame (263, 265, 304, 305) having a trench formed therein that defines a fluid sample cell (262, 324), wherein the trench includes a first sidewall and a second sidewall, a first electrode (264, 322) formed on the first sidewall, and a second electrode (266, 323) formed on the second sidewall such that the first and second electrodes are on opposite sides of the fluid sample cell (262, 324); and a frame (263, 265, 304, 305) having a trench formed therein that defines a fluid sample cell (262, 324), wherein the trench includes a first sidewall and a second sidewall, a first electrode (264, 322) formed on the first sidewall, and a second electrode (266, 323) formed on the second sidewall such that the first and second electrodes are on opposite sides of the fluid sample cell (262, 324); and a controller (150, 250) electrically connected to the sensor electrodes (264, 266, 322, 323) and the antenna (170, 270, 312), wherein the controller (150, 250) is configured to: (i) apply a voltage to the electrodes (264, 266, 322, 323) sufficient to generate a current through the electrodes (264, 266, 322, 323) related to a conductance of a fluid occupying the fluid sample cell (262, 324); (ii) measure the generated current; and (iii) use the antenna (170, 270, 312) to indicate the measured current.