A free program for Android, by App_Evolution.

Applock: Password Locker is an extremely powerful app locker, which can protect your device from unauthorized access and guard privacy. It allows you to lock apps with a password or pattern and spy camera. This applocker also prevents unwanted incoming calls. You can protect all apps and even system apps.

This applock also provides you with the tools to secure private photos and videos. To hide photos and videos, you can move them to a safe place. 

To ensure the security of your device, this applock will notify you if someone tries to open a locked app. If this happens, you will be able to take a picture of the intruder with the front camera and save the image in the device’s gallery.