What actually happens is they get close to the house with a radio scanner and read the code the key is giving out, then retransmit that code near the car. Nothing to do with wifi in the car. More recently manufacturers have instigated a feature that the key goes to sleep and stops transmitting when it detects no movement for a period of time.
I tested this with the misses T-Cross, full kessy, put the keys next to the door on a step, the car would happily open and close. Left them there, and 10 minutes later unable to unlock the door with the keys where they were resting but unmoved.