Just three conditions need to exist for it to work.
1. 7.1 installed and Summon enabled
2. Phone and fob need to be close together
3. You need to be 10' from your car
This last point still needs to be tested if you can be farther.
I have had it work from 20'.
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I discovered yesterday that if I ran summon in one direction and stopped the car short of its inherent distance limit, then summoned again without having entered the car, it traveled back to the original starting point and then stopped itself.