From PackRat Recipe Wiki

A lock is a gadget used to keep other items safe.

There are three ways to obtain a lock. You can buy one in any of the credit markets. You can draw one in a Bonus Draw (note that not every Bonus Draw contains a lock). Or you can MAKE a lock! Go to the gadgets page to find which cards can be used to make a lock.

Once you have a lock in your pack, click on "Gadgets" on the right hand of the screen. Click on the item you want locked as well as the lock itself. Click the dark blue "Use Gadget" button on the top right corner and your card will be safe for as long as you have it locked.

Note that the locks are only good for one use. Once a lock has been used, it will disappear, freeing up space in your pack.

If you lock an item up nobody can steal it. Locks are unbreakable. (In PackRat Classic, the locks were breakable.)