Send Help (https://sendhelp.tk) is a free and anonymous emergency messaging system.
Create an emergency messaging inbox, and when a message is received, you'll be notified via alerts that persist until the message is marked as read or deleted. Send Help is intended to be used for emergency situations, and as a result, it will override audio settings when a message is received and play an alert.
Send your family and friends your emergency inbox identifier so that they can contact you in an emergency. Never ignore or sleep through an emergency situation ever again.
You can also send messages to other Send Help users.