We don't have a simple way to wake-up on a threshold voltage but that is simple to implement with a comparator. This is an opamp where one input is connected to the voltage to measure and the other side to a threshold voltage. The output of the comparator goes to one of the digital inputs. You get an event if the threshold is met and you start measuring every 10mSec until your memory is full or until the voltage is blow the threshold.
You can store about 20Kb on a mcMod120 and 6Kb on a mcMod110.
If you have a power source don't have to use a comparator because you just keep measuring and don't store if the threshold is not met.

getting the data out can be done with MQTT. You can send the data to topic and have another application handle the data. The bandwidth to the gateway is about 1Kb per second. Everything you send out can be deleted.