Corrosion can be a problem for stainless steels in chloride-containing or other aggressive environments, especially when they are formed as components with complex shapes. Monitoring the corrosion performance of the stainless steels during their in-service life is not always an easy task. Traditional electrochemical cells can be difficult to adapt to complex surfaces, and undesired crevices or liquid electrolyte leaks can occur. In the presented work, the possible use of non-destructive techniques with innovative gel electrolytes was investigated using portable cells. The electrolytes were based on agar (used as a gelling agent with ionic conductivity), glycerol (a plasticizer that improves adaptability to complex surfaces), and NaCl or KClO4 salts (which improve the conductivity and control the aggression of the tests). X-ray photoelectron spectroscopy (XPS) and Mott–Schottky analysis were carried out to obtain information about the influence of the electrolyte on the passive layer. The oxygen concentration and conductivity in the gels with various glycerol contents were compared to those in liquid electrolytes. Electrochemical impedance spectroscopy (EIS) measurements were carried out in liquids and gels. The performance of the gel cell on a stainless-steel component with a weld and complex shape was checked. The variation in the sensitivity of gels with and without chlorides to identify corrosion-susceptible regions was tested.