An open padlock. "Something is open to you or available", or: "I'm going to uncover something that has been a secret up to now". Also possible: "Caution, this information is not secure!"
The unlocked emoji was introduced in 2010 and released as part of the Unicode 11.0 standard. This emoji can be found under the objects
category. Because the unlocked emoji has been around for quite some time, it should display correctly in the majority of operating systems.