Wi-Fi password recovery apps work by either using a previously stored password for a network or using one of a number of factory default passwords for certain routers. These apps cannot recover user-defined passwords for networks to which they have never been connected.
Many router and modern manufacturers ship their products with one of a number of default passwords. Often, users continue using this password without ever setting a unique password. Some Wi-Fi password recovery apps store a list of these default passwords in a database and try various ones until they achieve a connection.
Other password recovery apps work by storing the passwords of every Wi-Fi network to which they connect. When the user forgets a password, the app uses the stored password to connect to the network. Many mobile devices store network passwords automatically, so installing these apps is usually unnecessary. These apps cannot connect to new password-protected networks, nor can they connect to networks that have had their passwords changed since the previous successful connection.
Recovering a password for a network the device has never successfully connected with requires using specialized password recovery tools. These tools analyze data passing over a wireless network and then use a variety of password-cracking methods to find the password.