In this work, we fabricate and characterize an energy-efficient anomalous Hall sensor based on soft-magnetic FexPt1−x thin films with a large anomalous Hall angle. By varying the composition of the FexPt1−x alloy, its layer thickness and interfacial materials, the magnetization is tuned to be near the spin transition between the perpendicular and in-plane reorientations. We performed magneto-transport and noise characterizations on anomalous Hall sensors with a small sensing area of 20 × 20 µm2 in the 180 to 350 K temperature range. We found the best performance in a 1.25-nm-thick Fe0.48Pt0.52 sandwiched by two 1.6-nm-thick MgO layers at room temperature. The sensor has a large anomalous Hall angle of 1.95%. Moreover, it has the best field detectability of 237.5 nT/√Hz at 1 Hz and 15.3 nT/√Hz at 10 kHz, as well as a high dynamic reserve of 112.0 dB. These results suggest that the FexPt1−x alloy system is suitable for energy-efficient anomalous Hall sensors, particularly in micro-sensing applications.