user-1: Is an arduino password controlled lock safe or can the password be seen if they plug it in to a computer?

user6834: There are no passwords inherent to Arduino. You can implement them any way you want, resulting in any safety level from zero safely to nearly uncrackable.
Not so good: store the passwords straight in EEPROM. No protection of your data means that there's always a way to read them.
Quite safe: hash the password before storing it, for instance through SHA-512. Even if you can read the list of hashed passwords, it's pretty hard (read: nearly impossible) to reverse the algorithm to get the password back. For that reason SHA functions are called one-way functions. When you enter a password you run it through the SHA algorithm and check the hash against the list of hashes in EEPROM.

-1: <p>Is an arduino password controlled lock safe or can the password be seen if they plug it in to a computer?</p>
 6834: <p>There are no passwords inherent to Arduino. You can implement them any way you want, resulting in any safety level from zero safely to nearly uncrackable.</p>

<p><strong>Not so good</strong>: store the passwords straight in EEPROM. No protection of your data means that there's always a way to read them.</p>

<p><strong>Quite safe</strong>: hash the password before storing it, for instance through SHA-512. Even if you can read the list of hashed passwords, it's pretty hard (read: nearly impossible) to reverse the algorithm to get the password back. For that reason SHA functions are called one-way functions. When you enter a password you run it through the SHA algorithm and check the hash against the list of hashes in EEPROM.</p>
