A free program for Android, by PhotTools Studio.

AppLock is a powerful privacy guard that helps you to lock your apps and protect your phone from intruders. With this in your grasp, you can lock your most private apps such as WhatsApp, Instagram, Facebook, SMS, Contacts, Messenger, Settings, Gallery, Gmail, Browser, etc.

Security Lock – AppLock can transfer pictures and videos from Gallery to a photo/video vault with read/write external storage permission. You don’t have to worry about others seeing your private photos and videos with app lock.

The best part is that AppLock can secretly take pictures of those who try to unlock apps with wrong passwords in three attempts. So you can find out who are the curious ones!

The AppLock also has camera permission, which allows you to secretly capture the image of the intruder when someone tries to unlock apps with a wrong password.