If you have a jailbroken handset in your possession and you’re paranoid that someone might know your passcode and that they might be logging into your device when you aren’t looking, then you just might come to appreciate a newly-released and free jailbreak tweak dubbed LastUnlock by iOS developer Smokin1337.
As indicated by the screenshot example above, LastUnlock records the most recent date and time that your handset was unlocked (whether it was by you or someone else) and displays it on the Lock screen where the ‘press Home to unlock’ or ‘swipe up to unlock’ text would typically appear.