You assume here that you are aware of the fact that your device is in the hands of someone else.
I could ask you for your device under the pretense of making a phone call and then secretly transfer your account to my device. I could then secretly read your chats from my device and no one would be aware of it - until you check the amount of active sessions in settings.
I could ask you for your device under the pretense of making a phone call and then secretly transfer your account to my device. I could then secretly read your chats from my device and no one would be aware of it - until you check the amount of active sessions in settings.