The Pencils bluetooth airinterface is listening all the time like usual. As a Non-Human-Relation (NHR) it could be hepful in evidence. Not visible from outside for a suspect, not user-accessible to wipe it is one of few bluetooth mobile helpers which is accessible by the lightning and for cracking open. One may opose that any iBeacon device and equivalents is the same. Disagree. The Pencil has brain, algos and can talk (MMI Machine Machine Interface, iPad Pro to Pencil.
Who did forensics on the Pencil?
RoGu
The Pencil is talking over Bluetooth 4.1 (ifixit) and scans 240 times / second the iPad Pro force touch display. Observed that the Pencil is open for taling facing another bluetooth device (e.g. tablet). After a certain time the Pencil stops to announce and disappears on the bluetooth device.
A cortex CPU is next we should think.
RoGu