Based on David Middlecamp's fancy-asset-tracker demo for the Particle Electron with the Asset Tracker Shield.

The basic implementation provides a combined GPS and Mobile network location system that will:

• Wake up when accelerometer detects motion

• If more motion is detected

  • Reset 'no motion' shutdown timer
  • Initialise GPS module
  • Attempt to connect to Particle cloud

• If no status has been sent in more than 6 hours

  • Send idle_checkin status

• Read new NMEA sentences from the GPS module

• If we connected to the cloud but do NOT have a GPS fix

  • Retrieve an approximate location using the UBlox CellLocate feature (ULOC)
  • Use the GSM based location to hint the GPS module in hopes of a quicker fix timer using the PMTK740 and PMTK741 commands

• Publish the most accurate location we have to the Particle cloud.

  • If we have a GPS fix then use that, otherwise submit the approximate GSM location

• If GPS module has not gained a fix in 10 minutes (accelerometer will keep the tracker running permanently if it is in motion)

  • Turn off the GPS module for 10 minutes to save battery (yay active antenna)

• TODO: If battery SoC is less than 20%

  • Disable accelerometer based interrupts that keep the device awake
  • Rely on idle checkin every 6 hours (or longer? configurable maybe) to report location

• If we've not detected motion in more than 3 minutes

  • Put the Electron into deep sleep mode for 6 hours (or until woken by motion)

• Implement low-battery 'emergency' mode that only reports location every hours
• Implement ability to deep sleep the tracker for hours with no motion activated wakeup, e.g. when tracked device is being used by owner. Proximity based maybe?