<p>Laser fault injection (LFI) refers to a serious attack that modifies programs and data in embedded systems by introducing specific errors into a device in operation. As a countermeasure, in addition to duplication and optical sensors, the detection of LFIs using a sensor composed of digital circuits has recently been proposed. However, the research on the physical layout of these sensors is limited. In this work, we profile the laser irradiation position and its effect on the surrounding circuits by laser-scanning experiments on field-programmable gate arrays (FPGAs). Studies have shown that digital sensors with conventional designs have low-sensitivity areas with regard to LFIs. To improve LFI detection in FPGAs, we propose a design method for digital sensors and apply it to a ring oscillator (RO)-based digital sensor and a time-to-digital converter-based sensor. Experimental results show that the RO-based sensor based on the proposed method increased the area detecting LFI to about twice that of the conventional method, and detect 99.8% of the effective faults at the target register under protection. Furthermore, we extend the application of the RO-based sensor based on the proposed method to the protection of cryptographic circuits. The results of the laser-scanning experiment show that the proposed sensor detected 98.3% of the LFIs that caused effective faults in the cryptographic circuit.</p>