Window grilles offer the great advantage that you can leave the window open without major danger if you want to ventilate the room behind it. Window grilles are available in a wide variety of designs, the most common being permanently pre-installed window grilles and so-called flexible window grilles, which are individually adapted to the respective conditions. Window grilles, like other technologies and measures protecting against burglary and theft, are subdivided into Resistance Classes (German: Widerstandsklassen). Depending on the Resistance Class, the window grille protects against burglary attempts of varying severity.

In the private sector, Resistance Classes 1 (RC1) to 3 (RC3) are generally used – for burglary and property protection of commercial buildings, Resistance Classes 4 (RC4) to 6 (RC6) are recommended. Resistance class RC6 is the highest of all.

As a matter of principle, the bars of a window grille must be a maximum of 12 centimeters apart. Furthermore, the intersection points of the grille bars must be welded. Simple screwing is therefore not enough. The anchoring in the masonry must be robust and should not be easy to break out. A solid window grille must be fixed at a minimum of four points so that the house or building is very well protected against burglars.