What do I have to consider, when I want to use a stainless steel keyboard in the outdoor area?

Unfortunately, a general answer isn't possible in this case because it depends a lot on the installation situation. Gladly we send you a drawing that shows the proposed installation.

The sealing is obtained by an elastomer mat, mounted under the key caps.  

Although the penetration of liquid into the interior of the keyboard is prevented by this, it is possible, due to the construction, that liquid can penetrate under the key caps. This is irrelevant for the function, but can lead to icing in outdoor areas. That's why the usage in unprotected outdoor areas isn't advisable.

In addition to that, we want to indicate that examinations regarding the IP protection class have been done conforming to standards and that the hereby won results can't be extended directly on outdoor applications, because additional influences such as UV radiation, temperature fluctuations, weather etc must be considered, too.