Fischi,
From this post, I see you already have json2 loaded as a library.
[Link: remotecentral.com]Are you having some sort of specific error or were asking how to reference the value in the parsed object?
Here's how you would get the value you were asking for.
var obj = JSON.parse(responseText);
var myValue = obj.Devices[0].value;
Thanks,
Lyndel