Laser warning sensors (LWS) are critical components in modern electronic warfare and defense systems, designed to detect, identify, and alert against laser-based threats such as rangefinders, target designators, and beam-riding weapons. These sensors operate by capturing laser radiation across specific spectral bands, typically from ultraviolet to infrared, and analyzing the characteristics of the incoming laser pulses to determine threat parameters. The core principle involves photodetector arrays, which convert incident laser photons into electrical signals. These signals are then processed through high-speed analog and digital circuits to extract key features like wavelength, pulse repetition frequency (PRF), pulse width, and angle of arrival. Advanced LWS incorporate multi-sensor fusion, combining data from distributed optical apertures to enhance spatial coverage and reduce false alarms. Signal processing algorithms, including Fourier analysis and machine learning classifiers, are employed to discriminate between threat lasers and ambient optical noise from sources like sunlight or artificial lighting. Upon detection, the system generates real-time alerts and can interface with countermeasure systems—such as smoke grenade launchers or directional infrared countermeasures (DIRCM)—to initiate evasive or defensive actions. Modern trends focus on improving sensitivity and response time while minimizing size, weight, and power (SWaP) constraints. Integration with radar and missile warning systems further enhances situational awareness in complex battlefields. Challenges include coping with low-probability-of-intercept lasers and dense electromagnetic environments, driving ongoing research into quantum-based sensors and adaptive spectral filtering. Ultimately, laser warning sensors provide a vital layer of protection for military platforms, including aircraft, naval vessels, and armored vehicles, by enabling timely threat assessment and survivability enhancement.