Deadbolt. This lock type is considered to be the most secure one. These locks are sturdy and really hard to break. They can be single-cylinder or double-cylinder.

3 star cylinder locks are designed with anti-pick mechanisms, making it incredibly difficult for even the most skilled lock picker to manipulate the pins successfully.

A house key or residential door key will have a code like "LR-2" or "SR-1" on the head. Take the key to a hardware store and ask the key maker if they know what the letter and number designation on the key signifies. Keys usually are coded by type of lock they fit and this could identify old keys.

The key serves as a security token for access to the locked area; locks are meant to only allow persons having the correct key to open it and gain access. In more complex mechanical lock/key systems, two different keys, one of which is known as the master key, serve to open the lock.