A free program for Android, by Yajurved Developers.

If you want to allow access to your phone or tablet for just a single person, you can use the Face Lock app to prevent others from using your device if you want to let them access your phone or tablet for a limited amount of time.

The Face Lock app will allow you to keep children from accidentally purchasing in-app items or making unauthorized purchases, as well as keeping them safe from dangerous people. If you don’t want to let anyone else use your phone, the Face Lock app is the best way to ensure that your child doesn’t accidentally purchase items or make unauthorized purchases.