I'm not sure ..... with that scale, it can be almost anything .....
a pyrometer chip ..... an accelerometer / vibration sensor ..... a piezoceramic resonator .....
EDIT: @ Anselm, if i was not at home sleeping, it was really too easy, also cause i have one of them from an old HP scanner right in front of me now :crackup:
when you said RAVE, i thought ahhh some kind of LFO
ok, have a look at this.. this would fit in the palm of your hand, and its a mechanical device. Theres more to the pic which kinda will give it away, i'll reveal later if no one gets this.
It look as a high pressure spherical valve, for me (whatever you call it in English, in Italian is "rubinetto a sfera" or "valvola a sfera" ..... like, water tap ? ....., the sphere have a hole in the center and rotate for open and close the flow)
In alternative, it can be a "one-way fluid safety valve"