The massMass -production of fuelFuel -cell vehiclesFuel-cell vehicles and theVehicle eventual transition to the hydrogen economyHydrogen economy will require safe, inexpensive and reliable sensorsSensor capable of simultaneously detecting low concentrations of leaking hydrogenHydrogen and measuring broad ranges of hydrogenHydrogen concentration in storageStorage and energyEnergy generating systems. Although several competing sensorSensor technologies can potentially be used in this role, just a few of them have thus far demonstrated a combination of all desirable characteristics. This group of devices also includesMagneto-electronic sensors magneto-electronic sensorsSensor that can detect the presence of hydrogenHydrogen gas in a range of hydrogenHydrogen concentrations from approximately 0.05–100% at atmospheric pressureAtmospheric pressure with the response timeResponse time approaching the industryIndustry standard of one second. The hydrogen gas sensingHydrogen gas sensing mechanismMechanism underpinning the operation of magneto-electronic sensorsSensor is based on the physical processes of ferromagneticFerromagnetic resonanceMagneto-optical, magneto-opticalOptical Kerr effect and anomalous Hall effectAnomalous Hall effect that enable one to measure hydrogenHydrogen-induced changes in the magnetic propertiesMagnetic properties of structuresStructure combining Pd with one or several ferromagnetic metalsFerromagnetic metal such as Co, Fe or Ni. In this chapter, we overview the physical foundations of emergent ferromagneticFerromagnetic Pd-alloyAlloy-basedPd-alloy magneto-electronic hydrogen sensorsHydrogen sensor and compare their characteristics with those of high-performing multilayer thin filmThin films-based counterparts that have already demonstrated a potential to find commercialCommercial applicationsApplication.