The electronic combination lock uses a keypad that looks similar to a telephone keypad. The combination is entered one number at a time, like a telephone number. When the number is entered, a motor opens the lock. This type of lock is popular on safes and doors, but is almost never seen on padlocks. These locks require batteries or another source of electricity. There is sometimes a key backup in case the batteries die or the electronics fail. Most safe locks do not have a key backup, as a key backup can be picked. Most electronic locks allow the user to set the combination.