They see your WiFi presence and report it. Random Mac addresses help fight that, but if there is enough meta data on your phone they'll instantly link any mac address to you. Cell modems still connect and talk to towers without SIMs. It's a 911 feature. If Airplane mode really does disable everything, great. I don't trust Goggle given their history and recent lawsuit that showed they still tracked phones even when location was turned off.

Well shit.

My phone when I leave the house