YSK: if you’re calling someone’s cell phone during a late night emergency, call twice in quick succession. Usually this will override any “do not disturb” settings the recipient might have set up.
from /r/YouShouldKnow
YSK：如果你在深夜的紧急情况下拨打某人的手机，请连续拨打两次。通常这将覆盖收件人可能设置的任何 "请勿打扰 "设置。