A simple, novel and low cost optical device with the possibility of being integrated into a network of wireless sensors has been developed for the colorimetric detection of iron (II). The proposed device used is based on two light emitting diodes (LEDs) configured so that one acts as an emitter and the other as a light detector, and a simple threshold detection/timer circuit to measure the photocurrent at the detector LED. The colorimetric reaction is based on the chelating reaction of divalent iron with the ligand 1,10-phenanthroline. The calibration graph shows that the detection limit (DL) of iron (II) using this approach is 5 ppb with a RSD of 0.08%. All experiments were carried out in triplicate (N = 3). The effect of some cations on the determination of Fe (II) using the proposed method was also studied. Results found showed that the system is relatively free from interferences.