There is a convenient button on the screen of the app which allows you to send a message to the operator.
In addition to this, in the event that you have an emergency, you can inform the operator with just one touch of the + button.
This will very clearly alert the operator to the fact that you are having an emergency.
On iOS the emergency button is located on the map screen. The ‘Chat’ function is located in the menu (accessed using the arrow) and gives the option to send pre-set messages.