Completely turning off HP Prime

[Joe Horn]

Yes. What you want is called "Coma Mode" (different from "comma mode"). It puts your Prime into such a deep sleep that it's in a virtual coma, using almost no power at all. The batteries last much longer in coma mode than in normal off mode.

The easiest way to go into coma mode is:
(1) Press and keep holding down the Shift key.
(2) Press and hold down the On key for at least one second (very important!).
(3) Release both keys.

To exit coma mode, simply press On and wait a few seconds. The delay might scare you... it always makes me fear that the Prime has crashed... but it's normal. Just be patient, and it'll power up.