In some regions, you can make emergency calls from
HTC One even if you don’t have a SIM card installed or your SIM card has been blocked.
Important: If you don't have a network signal, you won't be able to make an emergency call.
Dial the emergency number for your locale, and then tap
Tip: If you've enabled but forgotten your lock password or lock pattern, you can still make emergency calls by tapping
Emergency call on the screen.