Again some story with a messenger:
during a security relevant mission, messenger crashed apparently and display frozen.
it did switch off itself when battery empty
battery was charged then and device taken back into operation. After few minutes, it started to transmit sos by itself, no interaction from user. Emergency center did replay to the unit as expected, but was unable to get valid position. User informed, managed to switch the device off finally.
Slightly I have doubt that this devices are of any use at all. Have just ordered some more for further testing, but when a device fails in such way during a really security relevant mission, it can not be used any more.