Anybody knows what this component is? (The white cylinder.)
It has to be some kind of switch since it is marked as "S2", but I never saw anything like it before.
That is a kind of motion detector.
Picture from the datasheet:
They are meant to be used in devices that should sleep when not in use, but wake up and do something when moved.
Like a GPS tracker. You want to record where your cat goes, but don't need 18 hours a day of unchanging GPS coordinates from all the naps it takes. When the cat naps, no signals from the sensor. When your cat gets up, the sensor "rattles" its output and your GPS receiver wakes up and takes notes.
That sensor is entirely passive, so it doesn't use battery power like many other kinds of motion detectors. Well, unless you count 50nA as wasting power.