It is a reed capsule (aka "reed switch") a switch which closes when a magnet is nearby). Replacements can be purchased inexpensively from online retailers- probably something that is similar in physical size will work.
It may be to detect the presence of the inhalation chamber but I'm not sure of the way these things work. Something like a float with a magnet in it is also possible. I suspect it will be obvious to you upon inspection.