Regarding the above the notecard already has this feature, though not exactly as you describe.
GPS is very power hungry - a single GPS fix consumes the same amount of power as multiple days of standby operation, and ,surprisingly, a GPS fix consumes more power than transmitting that fix to Notehub.
Therefore if there is no motion (as measured by the accelerometer) the Notecard assumes it has remained in place and does not turn on the GPS. Periodic reporting of this type (I’m still here) is referred to as the heartbeat and is enabled using card.location.track:
The configuration shown below will capture and sync GPS once every 10 minutes when there is motion, and will send a heartbeat once per hour when no motion is detected.