I am notorious for locking my keys in the car. (autolist.com)
There's a centralized power / lock key on the right of the handset which also houses the fingerprint scanner, while on the left two small circular buttons provide volume control. (techradar.com)
There is one more way to take a screenshot of your device, i.e., press the power / lock key along with the home key. (phoneradar.com)