The Lithium555 by Flexopower offers a unique user safety protection feature.
The Lithium555 is lockable, which means that there is no AC and DC output when locked, even if a button is pressed. To unlock, you first have to press both buttons for 3 seconds. Only then can the AC and DC outputs be switched on. This is a great feature if the Lithium555 is left unsupervised or around children and impaired persons.
Here is a video visualizing the process: