Nitrophone 4 Strange (security warning?!) sounds

Hi all,

i bought a Nitrophone 4 and after an automatically triggered restart (over night) the phone is making an alarm noise when entering a pin code.
This high sound, rings out for around 3 seconds for each input i do.

My Question: What does this mean and is this a sign to NOT Enter any Pin Codes because of a potential securitiy problem?

Thank you all for helping me :slightly_smiling_face: