It mentions integrating with your phone's do not disturb functions. Usually in an emergency someone will call you multiple times in a row and, presumably, this would open the shell.
And unless you live alone, which many don't, other people will usually have phones.
You can also buy a dumb phone specifically for emergencies, 911 doesn't require a paid line.
And like other's said, you can probably pry that sucker open. It looks flimsy honestly, with no lock or dead bolt connecting the two parts in the front...