Hi, the keys are securely stored on to the device on a dual chip secure element. There is a 4 or 8 digit pin code on ledger nano s so you can only open it if in case you enter 3 times wrong pin it will format/wipe the device and you need to setup it again using the 24-word key words which you need to note down initially while setting up the device at first time usage. Again, if you loose the device you can buy a new one any using your recovery seed words you can get your device back in same condition. Hope it helps :)