The secret is making a key to fit the particular lock it's supposed to open (or close). Instead of merely replicating a key by grinding the contours of the original onto a blank (which tends to produce tiny errors each time the key is copied), Shloosl analyzes the depth of the teeth on the original, makes deductions about the lock it operates, and cuts the key with the width and spacing according to the specifications of the lock manufacturer (you can read more about their process here).
All that's needed is a high-res image of your key, taken with your phone, and then emailed to the company. For a cost of $5, Shloosl will then send you a duplicate in the mail. Visit their site for more info, including their security precautions.