The gate at the back of the house uses an optical sensor (from Metrodyns) to stop the gate closing if there's anything in the way. It won't stay open on itself indefinitely though, which is sometimes necessary. This small cover will fool the sensor into keeping the gate open.

There's a second version that has the text “Toröffner” cut out of it.

The sensor's dimensions are 600x296x714mm. The fit is anything but snug, but since the cover just rests on top, it isn't necessary.