The phones wont unlock if your eyes are closed. So that's kinda already a feature. Of course a full "lock out because this is my distress signal" feature would

The phones wont unlock if your eyes are closed. So that's kinda already a feature. Of course a full "lock out because this is my distress signal" feature would be nifty, but imagine you blink in the middle of unlocking your phone on a regular day and find yourself very locked out. That'd be very annoying.