SOS function very poorly resolved: no communication with the help of caller

I wanted to use the tracker as an SOS call for Grandpa. Where this would be possible: Three direct dial numbers with AC / speakerphone, location query, battery life for several days ..... everything is ok and easy to use.

Unfortunately, the function of the main key, the emergency button, very poor:
If the caller presses the help emergency button, an SMS is sent to the location coordinates to the registered number and this number will be called at the same time. After removing the aid caller is unfortunately only to hear. It is not possible to talk to him, because the tracker does not go into the mode Feisprechen. It has no way to communicate with the help crying. Absolutely incomprehensible why the tracker is configured.